1988 BMW 3 SERIES Idle speed

0•9Roadside Repairs
When jump-starting a car using a
booster battery, observe the following
precautions:
4Before connecting the booster
battery, make sure that the ignition is
switched off.
4Ensure that all electrical equipment
(lights, heater, wipers, etc) is
switched off.
4Make sure that the booster battery is
the same voltage as the discharged
one in the vehicle.
4If the battery is being jump-started
from the battery in another vehicle,
the two vehcles MUST NOT TOUCH
each other.
4Make sure that the transmission is in
neutral (or PARK, in the case of
automatic transmission).
Jump starting will get you out
of trouble, but you must correct
whatever made the battery go
flat in the first place. There are
three possibilities:
1The battery has been drained by
repeated attempts to start, or by
leaving the lights on.
2The charging system is not working
properly (alternator drivebelt slack
or broken, alternator wiring fault or
alternator itself faulty).
3The battery itself is at fault
(electrolyte low, or battery worn out).
Connect one end of the red jump lead to
the positive (+) terminal of the flat
batteryConnect the other end of the red lead to
the positive (+) terminal of the booster
battery.Connect one end of the black jump lead
to the negative (-) terminal of the
booster battery
Connect the other end of the black
jump lead to a bolt or bracket on the
engine block, well away from the
battery, on the vehicle to be started.
123
4
Make sure that the jump leads will not
come into contact with the fan, drive-
belts or other moving parts of the
engine.5
Start the engine using the booster
battery, then with the engine running at
idle speed, disconnect the jump leads in
the reverse order of connection.6
Jump starting

1
Engine
Oil filter
M10 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Champion C121
M20 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Champion C160
M30 engines
3-Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Champion C160
5-Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Champion X115
M40 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Champion X120
Valve clearances (intake and exhaust)
M10 engines
Cold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.20 mm
Hot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.25 mm
M20 engines
Cold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.25 mm
Hot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.30 mm
M30 engines
Cold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.30 mm
Hot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.35 mm
M40 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hydraulic adjusters
Cooling system
Antifreeze mixture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40% antifreeze/60% water
Chapter 1
Routine maintenance and servicing
Air filter renewal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Automatic transmission fluid and filter change . . . . . . . . . . . . . . . . . 28
Automatic transmission fluid level check . . . . . . . . . . . . . . . . . . . . . 8
Battery check, maintenance and charging . . . . . . . . . . . . . . . . . . . . 13
Brake system check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Cooling system - draining, flushing and refilling . . . . . . . . . . . . . . . . 29
Cooling system check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Differential lubricant change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Differential lubricant level check . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Driveshaft gaiter check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Drivebelt check, adjustment and renewal . . . . . . . . . . . . . . . . . . . . . 11
Engine idle speed and CO level check and adjustment . . . . . . . . . . 12
Engine oil and filter change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Engine timing belt renewal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Exhaust system check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Evaporative Emissions Control (EVAP) system check . . . . . . . . . . . 33
Fluid level checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Fuel filter renewal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Fuel system check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Manual transmission lubricant change . . . . . . . . . . . . . . . . . . . . . . . 31
Manual transmission lubricant level check . . . . . . . . . . . . . . . . . . . . 16
Power steering fluid level check . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Routine maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Service light resetting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Spark plug check and renewal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Spark plug HT leads, distributor cap and rotor - check
and renewal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Steering and suspension check . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Throttle linkage - check and lubrication . . . . . . . . . . . . . . . . . . . . . . 19
Tyre and tyre pressure checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Tyre rotation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Tune-up general information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Underbonnet hoses - check and renewal . . . . . . . . . . . . . . . . . . . . . 10
Valve clearances - check and adjustment . . . . . . . . . . . . . . . . . . . . 18
Wiper blades - check and renewal . . . . . . . . . . . . . . . . . . . . . . . . . . 27
1•1
Easy,suitable for
novice with little
experienceFairly easy,suitable
for beginner with
some experienceFairly difficult,
suitable for competent
DIY mechanic
Difficult,suitable for
experienced DIY
mechanicVery difficult,
suitable for expert
DIY or professional
Degrees of difficulty
Specifications Contents

Fuel system
Idle speed
3-Series, E30
316 with M10/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 850 ± 50 rpm
316i with M40/B16 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800 ± 40 rpm
318i with M10/B18 engine (manual transmission) . . . . . . . . . . . . . 850 ± 50 rpm
318i with M10/B18 engine (automatic transmission) . . . . . . . . . . . 750 ± 50 rpm
318i with M40/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800 ± 40 rpm
320i with M20/B20 engine (L-Jetronic) . . . . . . . . . . . . . . . . . . . . . . 800 ± 50 rpm
320i with M20/B20 engine (Motronic) . . . . . . . . . . . . . . . . . . . . . . . 760 ± 40 rpm
325i with M20/B25 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 760 ± 40 rpm
5-Series, E28 (“old-shape”)
518 and 518i with M10/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . 800 ± 50 rpm
All other models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 850 ± 50 rpm
5-Series, E34 (“new-shape”)
518i with M40/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800 ± 40 rpm
520i with M20/B20M engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 760 ± 40 rpm
525i with M20/B25M engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 760 ± 40 rpm
530i with M30/B30M engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800 ± 50 rpm
535i with M30/B35M engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 850 ± 50 rpm
CO% at 3000 rpm
3-Series, E30
316 with M10/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5 to 1.0
316i and 318i with M40/B16 engine . . . . . . . . . . . . . . . . . . . . . . . . 0.7 ± 0.5
318i with M10/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.0 maximum
320i with M20/B20 engine (L-Jetronic) . . . . . . . . . . . . . . . . . . . . . . 1.0 ± 0.5
320i with M20/B20 engine (Motronic) . . . . . . . . . . . . . . . . . . . . . . . 0.7 ± 0.5
325i with M20/B25 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.0 ± 0.5
5-Series, E28 (“old-shape”)
518 and 518i with M10/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . 1.0 maximum
525i with M30/B25 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.0 ± 0.5
528i with M30/B28 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 maximum
535i with M30/B34 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.3 to 1.5
M535i with M30/B34 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.3 to 1.5
5-Series, E34 (“new-shape”)
All models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.7 ± 0.5
Air filter element
M10 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Champion W155 (round) or U504 (square)
M20 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Champion U504 or U527
M30 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Champion U504 or U527
M40 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Champion U527
Fuel filter (all fuel injection engines) . . . . . . . . . . . . . . . . . . . . . . . . . . . . Champion L206
Ignition system
Spark plug type
M10, M20 and M30 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Champion N9YCC
M40 engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Champion C9YCC
Spark plug gap* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.8 mm
Spark plug (HT) leads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Champion type not available
* The spark plug gap quoted is that recommended by Champion for their specified plugs listed above. If spark plugs of any other type are to be
fitted, refer to their manufacturer’s spark plug gap recommendations.
Brakes
Disc brake pad thickness (minimum) . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0 mm
Drum brake shoe lining thickness (minimum) . . . . . . . . . . . . . . . . . . . . . 2.0 mm
Wiper blades
Windscreen
3-Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Champion X-5103
3-Series passenger side from 1991 . . . . . . . . . . . . . . . . . . . . . . . . . . Champion X-5103 (20 inch) or Champion X-5303 (21 inch)
5-Series, E28 (“old-shape”) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Champion X-4503
5-Series, E34 (“new-shape”) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Champion type not available
Tailgate
3-Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Champion X-4503
5-Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Champion type not available
1•2Servicing Specifications

Maintenance schedule
The following maintenance intervals are based on the assumption
that the vehicle owner will be doing the maintenance or service work,
as opposed to having a dealer service department do the work.
Although the time/mileage intervals are loosely based on factory rec-
ommendations, most have been shortened to ensure, for example, that
such items as lubricants and fluids are checked/changed at intervals
that promote maximum engine/driveline service life. Also, subject to
the preference of the individual owner interested in keeping his or her
vehicle in peak condition at all times, and with the vehicle’s ultimate
resale in mind, many of the maintenance procedures may be
performed more often than recommended in the following schedule.
We encourage such owner initiative.
When the vehicle is new, it should be serviced initially by a factory-
authorised dealer service department, to protect the factory warranty.
In many cases, the initial maintenance check is done at no cost to the
owner (check with your dealer service department for more
information).
1•4Maintenance and servicing
Every 250 miles or weekly, whichever
comes first
m mCheck the engine oil level (Section 4)
m mCheck the engine coolant level (Section 4)
m mCheck the brake fluid level (Section 4)
m mCheck the clutch fluid level (Section 4)
m mCheck the washer fluid level (Section 4)
m mCheck the tyres and tyre pressures (Section 5)
Every 6000 miles or 6 months,
whichever comes first
All items listed above, plus:
m mChange the engine oil and oil filter (Section 6)
m mCheck the power steering fluid level (Section 7)
m mCheck the tyres, and rotate if necessary (Section 9)
m mCheck the automatic transmission fluid level
(Section 8)
m mCheck the underbonnet hoses (Section 10)
m mCheck/adjust the drivebelts (Section 11)
m mCheck engine idle speed and CO (Section 12)
Every 12 000 miles or 12 months,
whichever comes first
All items listed above, plus:
m mCheck/service the battery (Section 13)
m mCheck the spark plugs (Section 14)
m mCheck/renew the HT leads, distributor cap and
rotor (Section 15)
m mCheck/top-up the manual transmission lubricant
(Section 16)
m mCheck the differential oil level (Section 17)
m mCheck the valve clearances, and adjust if
necessary - does not apply to M40 engines
(Section 18)
m mCheck and lubricate the throttle linkage (Section 19)
m mRenew the air filter (Section 20)
m mCheck the fuel system (Section 21)
m mInspect the cooling system (Section 22)
m mInspect the exhaust system (Section 23)
m mInspect the steering and suspension components
(Section 24)
m mCheck the driveshaft gaiter(s) (Section 25)
m mInspect the brakes (Section 26)
m mInspect/renew the windscreen wiper blades
(Section 27)
Every 24 000 miles or 2 years,
whichever comes first
All items listed above plus:
m mChange the automatic transmission fluid and filter
(Section 28)
m mDrain, flush and refill the cooling system (Section 29)
m mRenew the spark plugs (Section 14)
m mCheck/renew the spark plug HT leads (Section 15)
m mRenew the fuel filter (Section 30)
m mChange the manual transmission lubricant (Section 31)
m mChange the differential oil (Section 32)
m mCheck the evaporative emissions system, where
applicable (Section 33)
m mReset the service indicator lights (Section 34)
m mRenew brake fluid by bleeding (see Chapter 9)
m mCheck the handbrake operation (see Chapter 9)
Every 60 000 miles
m
mRenew the timing belt (Section 35)

move the component away from the engine to
tighten the belt, or towards the engine to
loosen the belt. Hold the accessory in
position, and check the belt tension. If it is
correct, tighten the two bolts until just tight,
then recheck the tension. If the tension is still
correct, tighten the bolts.
8It will often be necessary to use some sort
of lever to move the accessory while the belt
is adjusted. If this must be done to gain the
proper leverage, be very careful not to
damage the component being moved, or the
part being prised against.
Renewal
9To renew a belt, follow the instructions
above for adjustment, but remove the belt
from the pulleys.
10In some cases, you will have to remove
more than one belt, because of their
arrangement on the front of the engine.
Because of this, and the fact that belts will
tend to fail at the same time, it is wise to
renew all belts together. Mark each belt and
its appropriate pulley groove, so all renewed
belts can be fitted in their proper positions.
11It is a good idea to take the old belts with
you when buying new ones, in order to make
a direct comparison for length, width and
design.
12Recheck the tension of new belts after a
few hundred miles.
12 Engine idle speed and CO
level check and adjustment
4
Note:The engine should be at normal
operating temperature, with correct ignition
timing and valve clearances (where
adjustable). The air filter should be in good
condition, and all electrical components
(including the air conditioning, where fitted)
should be switched off.
Carburettor
1Connect a tachometer and exhaust gas
analyser (CO meter) to the engine.
2Start the engine and allow it to idle.
3Check that the idle speed is as given in the
Specifications. Adjustment of the idle speed is
only possible on the 2B4 carburettor. Turn the
carburettor idle speed adjustment screw until
the engine idles at the correct speed (see
illustration).
4If the idle speed is low on the 2BE
carburettor, and all wiring to the carburettor is
in good condition, it is possible to connect a
resistance into the control circuit. This should
be carried out by your BMW dealer.
5Check that the CO reading is as given in the
Specifications. If not, turn the carburettor idle
mixture adjustment screw until the mixture is
correct (see illustration).
L-Jetronic
6Connect a tachometer and CO meter to the
engine. BMW technicians use a special CO
tester with a probe connected into the
exhaust manifold, but the normal type of
tester which locates in the exhaust tailpipe
can be used instead. Note however that on
models with a catalytic converter, meaningful
CO readings will not be obtained at the
tailpipe.
7Start the engine and allow it to idle.
8Check that the idle speed is as given in
Specifications. If not, remove the tamperproof
cap from the throttle housing, and turn the idle
adjustment screw until the speed is correct.
9Check that the CO reading is as given in the
Specifications. The mixture control screw is
located on the airflow meter, and a specialtool (BMW number 13 1 060) may be required
to make the adjustment.
Motronic
10Connect a tachometer and CO meter to
the engine. BMW technicians use a special
CO tester with a probe connected into the
exhaust manifold, but the normal type of
tester which locates in the exhaust tailpipe
may be used instead. Note however that on
models with a catalytic converter, meaningful
CO readings will not be obtained at the
tailpipe.
11It is not possible to adjust the idle speed
manually, as the idle air stabiliser valve is
activated by the electronic control unit. If the
idle speed is not within the specified range
with the engine at normal operating
temperature, check for a leak in the air inlet
system, and also check the operation of the
idle air stabiliser valve (see Chapter 4).
12Check that the CO reading is as given in
the Specifications. If adjustment is required,
prise out the tamperproof plug from the
airflow meter, and turn the adjustment screw
to set the CO content (on some models, an
Allen key will be required). Fit a new
tamperproof plug on completion (see
illustrations).
1•15
12.12a Removing the tamperproof plug
from the airflow meter
12.5 Mixture adjustment screw (2) on the
2B4 carburettor
12.3 Idle speed adjustment screw on the
2B4 carburettor (shown with the
carburettor removed)
12.12b Adjusting the CO on the Motronic
system
1
Every 6000 miles

4
Carburettor (Solex 2B4)
Main jet
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . X120
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . X90
Air correction jet
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Venturi diameter
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 mm
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 mm
Idle/air jet
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50/120
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40/125
Float needle valve diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0 mm
Choke gap (pulldown) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.0 to 5.5 mm
Throttle positioner spring preload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.0 to 24.0 mm
Float level
Stage 1 float chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27.0 to 29.0 mm
Stage 2 float chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29.0 to 31.0 mm
Chapter 4 Fuel and exhaust systems
Accelerator cable - check, adjustment and renewal . . . . . . . . . . . . . 9
Air cleaner assembly - removal and refitting . . . . . . . . . . . . . . . . . . . 8
Air filter renewal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . See Chapter 1
Airflow meter - check, removal and refitting . . . . . . . . . . . . . . . . . . . 16
Carburettor - cleaning and adjustment . . . . . . . . . . . . . . . . . . . . . . . 12
Carburettor - general information . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Carburettor - removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Cold start injector and thermotime switch -
checkand renewal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Engine idle speed check and adjustment . . . . . . . . . See Chapter 1
Exhaust system check . . . . . . . . . . . . . . . . . . . . . . . . See Chapter 1
Exhaust system servicing - general information . . . . . . . . . . . . . . . . 22
Fuel filter renewal . . . . . . . . . . . . . . . . . . . . . . . . . . . See Chapter 1
Fuel injection system - check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Fuel injection system - depressurising . . . . . . . . . . . . . . . . . . . . . . . 2Fuel injection system - fault finding . . . . . . . . . . . . See end of Chapter
Fuel injection - general information . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Fuel injection systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Fuel injectors - check and renewal . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Fuel lines and fittings - repair and renewal . . . . . . . . . . . . . . . . . . . . 5
Fuel pressure regulator - check and renewal . . . . . . . . . . . . . . . . . . 18
Fuel pump, transfer pump and fuel level sender unit -
removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Fuel pump/fuel pressure - check . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Fuel system check . . . . . . . . . . . . . . . . . . . . . . . . . . . See Chapter 1
Fuel tank - removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Fuel tank cleaning and repair - general information . . . . . . . . . . . . . 7
General information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Idle air stabiliser valve - check, adjustment and renewal . . . . . . . . . 21
Throttle body - check, removal and refitting . . . . . . . . . . . . . . . . . . . 17
4•1
Easy,suitable for
novice with little
experienceFairly easy,suitable
for beginner with
some experienceFairly difficult,
suitable for competent
DIY mechanic
Difficult,suitable for
experienced DIY
mechanicVery difficult,
suitable for expert
DIY or professional
Degrees of difficulty
Specifications Contents

information on removing and refitting the
intake manifold, refer to Chapter 2A.
The throttle valve inside the throttle body or
carburettor is actuated by the accelerator
cable. When you depress the accelerator
pedal, the throttle plate opens and airflow
through the intake system increases.
On fuel injection systems, a flap inside the
airflow meter opens wider as the airflow
increases. A throttle position switch attached
to the pivot shaft of the flap detects the angle
of the flap (how much it’s open) and converts
this to a voltage signal, which it sends to the
computer.
Fuel system
On carburettor models, the fuel pump
supplies fuel under pressure to the
carburettor. A needle valve in the float
chamber maintains the fuel at a constant
level. A fuel return system channels excess
fuel back to the fuel tank.
On fuel injection models, an electric fuel
pump supplies fuel under constant pressure
to the fuel rail, which distributes fuel to the
injectors. The electric fuel pump is located
inside the fuel tank on later models, or beside
the fuel tank on early models. Early models
also have a transfer pump located in the fuel
tank. The transfer pump acts as an aid to the
larger main pump for delivering the necessary
pressure. A fuel pressure regulator controls
the pressure in the fuel system. The fuel
system also has a fuel pulsation damper
located near the fuel filter. The damper
reduces the pressure pulsations caused by
fuel pump operation, and the opening and
closing of the injectors. The amount of fuel
injected into the intake ports is precisely
controlled by an Electronic Control Unit (ECU
or computer). Some later 5-Series models
have a fuel cooler in the return line.
Electronic control system (fuel
injection system)
Besides altering the injector opening
duration as described above, the electronic
control unit performs a number of other tasks
related to fuel and emissions control. It
accomplishes these tasks by using data
relayed to it by a wide array of information
sensors located throughout the enginecompartment, comparing this information to
its stored map, and altering engine operation
by controlling a number of different actuators.
Since special equipment is required, most
fault diagnosis and repair of the electronic
control system is beyond the scope of the
home mechanic. Additional information and
testing procedures for the emissions system
components (oxygen sensor, coolant
temperature sensor, EVAP system, etc.) is
contained in Chapter 6.
2 Fuel injection system-
depressurising
1
Warning: Fuel is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. Don’t
smoke or allow open flames or bare light
bulbs near the work area. Also, don’t work
in a garage where a natural gas-type
appliance with a pilot light is present.
1Remove the fuel pump fuse from the main
fuse panel (see illustrations). Note:Consult
your owner’s handbook for the exact location
of the fuel pump fuse, if the information is not
stamped onto the fusebox cover.
2Start the engine, and wait for it to stall.
Switch off the ignition.
3Remove the fuel filler cap to relieve the fuel
tank pressure.
4The fuel system is now depressurised.
Note:Place a rag around fuel lines before
disconnecting, to prevent any residual fuel
from spilling onto the engine(see
illustration).
5Disconnect the battery negative cable
before working on any part of the system.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
3 Fuel pump/fuel pressure-
check
3
Warning: Fuel is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. Don’t
smoke, or allow open flames or bare light
bulbs, near the work area. Also, don’t work
in a garage where a natural gas-type
appliance with a pilot light is present.
Carburettor engines
1To test the fuel pump, it will be necessary to
connect a suitable pressure gauge between
the fuel pump outlet, and the carburettor
supply pipe. For this particular test, the fuel
return valve, which is normally connected in
the fuel line from the fuel pump to the
carburettor, mustbe bypassed.
2With the engine running at idle speed, the
pump pressure should be between 0.1 and
0.3 bars.
3Should a pressure gauge not be available, a
simpler (but less accurate) method of testing
the fuel pump is as follows.
4Disconnect the outlet hose from the fuel
pump.
5Disconnect the LT lead from the coil, to
prevent the engine firing, then turn the engine
over on the starter. Well-defined spurts of fuel
should be ejected from the outlet hose.
Fuel injection engines
Note 1:The electric fuel pump is located
inside the fuel tank on later models, or beside
the fuel tank on early models. Early models are
also equipped with a transfer pump located in
the fuel tank. The transfer pump feeds the
main pump, but can’t generate the high
pressure required by the system.
Note 2:The fuel pump relay on Motronic
systems is activated by an earth signal from
the Motronic control unit (ECU). The fuel
pump operates for a few seconds when the
ignition is first switched on, and then
continues to operate only when the engine is
actually running.
Fuel and exhaust systems 4•3
2.4 Be sure to place a rag under and
around any fuel line when disconnecting2.1b Removing the fuel pump fuse on
5-Series models2.1a Removing the fuel pump fuse on
3-Series models
4

9Remove the screws securing the throttle
housing to the main body (see illustration).
10Prise out the intermediate throttle link. If
this proves difficult, unscrew the nut and
disconnect the lever from the primary throttle
spindle, taking care not to disturb the return
spring (see illustration).
11Separate the throttle housing from the
main body, and remove the gasket (see
illustrations).
12With the cover inverted, tap out the float
pivot pins, remove the floats, and lift out the
two needle valves - keeping all the
components identified side for side (see
illustrations).
13Unscrew the bypass fuel jet from the
secondary float chamber, then similarly
remove the jets from the cover - keeping them
all identified for location (see illustrations).
14Clean all the components, and blow all
the internal channels clear using low air
pressure.
15Reassembly is a reversal of dismantling,
but note the following points:
a) Fit the new gaskets and seals supplied in
the repair kit.
b) Before refitting the cover, check that the
choke linkage arm is correctly located in
the lever (see illustration).
c) Check and if necessary adjust the float
settings. Invert the cover, and check thedistance from the contact face (without
gasket) to the top of the float, making sure
that the needle valve spring-tensioned
ball is not depressed (see illustration).
Note that the dimension is different for
the primary and secondary floats (see
Specifications). If adjustment is
necessary, bend the float arm as required.
d) Make sure that the seal is fitted to the top
of the accelerator pump (see
illustration).
Adjustment
Note:Idle speed and mixture adjustments are
covered in Chapter 1.
Automatic choke (2B4)16Check that the automatic choke cover
and housing alignment marks are clearly
visible; if not, make new marks.
17Remove the three screws and withdraw
the metal ring (see illustration).
18Remove the plastic cover, at the same
time disengaging the bi-metal spring from the
control lever (see illustration).
19Fit a rubber band to the bottom of the
control lever. Push the pulldown lever to the
right and use a 4.2 mm diameter drill to check
the distance between the lower edge of the
choke valve and the wall of the carburettor(see illustration). Alternatively apply vacuum
to the pulldown unit to move the lever.
20If adjustment is necessary, turn the screw
on the end of the pulldown unit (see
illustration).
21Refit the cover in reverse order, making
sure that the alignment marks are in line.
Throttle positioner (2B4)
22With the throttle in the idle position, check
that the length of the spring on the throttle
positioner is 23.0 ± 1.0 mm. If not, adjust the
nut as required.
23With no vacuum applied (engine stopped)
check that the control travel, measured
between the stop screw and lever, is 5.0 ±
0.5 mm. If necessary, loosen the locknut and
turn the diaphragm rod as required. Tighten
the locknut on completion.
Fuel and exhaust systems 4•13
12.15b To check the float level, measure
the distance between the contact face and
the top of the float12.15a Choke linkage arm located in the
automatic choke lever
12.20 If adjustment is necessary, turn the
screw (arrowed) on the end of the
pulldown unit
12.19 Fit a rubber band (2) to the bottom
of the control lever, then push the
pulldown lever to the right, and use a
4.2 mm diameter drill (1) to check the
distance between the lower edge of the
choke valve and the wall of the carburettor
12.17 Remove the three screws and
withdraw the metal ring
12.15c Accelerator pump seal (arrowed)
12.18 Remove the automatic choke cover,
at the same time disengaging the bi-metal
spring from the control lever
4