1999 AUDI A4 check engine

24-30

When the engine is idling the engine control
module tries constantly to adjust the actual
engine speed so that it matches the specified
value.
This means that the actual engine speed when
idling should always be approximately the same
as the specified engine speed.
Display fields 3 and 4 provide additional
information which is not relevant when checking
the idle speed.

-
Press button.

- Press buttons -0- and -6- to select function "End
Output" and confirm entry with -Q- button.

- If readout does not match Specified value, check
DTC memory again.

- If DTC memory was erased, generate readiness
code Page 01
-105
.
Pa
ge 35 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1

24-31

If the idle speed is too high or too low, or if
the engine does not idle smoothly, and there
are no malfunctions stored in the DTC
memory, carry out the following tests
(marked with dots):

Check intake system for un-metered air (air
leaks) Page 24
-76
.

Check Throttle Valve Control Module
Page 24
-139
.

EVAP canister purge regulator valve
constantly open, check Page 24
-134
.

Adaptation of Throttle Valve Control Module
Page 24
-146
.
Pa
ge 36 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1

24-33

Fuel pressure regulator and residual
fuel pressure, checking


Requirements

Fuel pump relay OK
Fuel pump OK
Fuel filter OK
Battery voltage at least 11 V

Note:
The fuel pressure regulator regulates the fuel
pressure according to intake manifold pressure.
This ensures that the drop in pressure at the
injectors remains the same throughout all engine
speed and engine load ranges.

WARNING!

Fire hazard! The fuel system is pressurized.
Before loosening hose connections or
opening the test connection (to measure fuel
pressure), place a cloth around the
connection. Then release pressure by
carefully pulling off the hose or cap.
Pa
ge 38 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
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24-34

Testing system pressure

Note:
If fuel flows out at the vacuum connection on the fuel pressure regulator
during the following pressure test, fit a new fuel pressure regulator. - Connect pressure gauge VAG 1318 to supply pipe using adapters
1318/7, 1318/8 (pressure hose) and 1318/15.
- Disconnect vacuum hose between fuel pressure regulator and intake
manifold at fuel pressure regulator end; seal off end of hose.
- Start engine and run at idling speed.
- Measure fuel pressure.
Specified value: approx. 3.8...4.2 bar
- If fuel pressure does not match specification, install a new fuel
pressure regulator for test purposes and repeat pressure test.
- If fuel pressure still does not match specification, check fuel pump and
supply pipe for damage (e.g. pinching) and replace if necessary.
Pa
ge 39 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1

24-35

- If pressure is higher than specification, check
return pipe for damage (e.g. pinching) and
renew if necessary.

Note:
During the following test, do not allow the engine
to run for too long with the vacuum hose
disconnected, otherwise the increased fuel
pressure will enrich the air/fuel mixture and may
cause the lambda control limits to be exceeded.
This would be stored as a fault in the fault
memory.

- Start the engine and run at idling speed.

- Switch off electrical consumers (air conditioner
etc.).

- Re-connect vacuum hose to fuel pressure
regulator and observe drop in pressure on
pressure gauge.
Pa
ge 40 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
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11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
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e=re
pair&id=AUDI.B5.FU04.24.1

24-36

- When the vacuum hose is re-connected the fuel
pressure should drop by around 0.5 bar.

If the pressure does not change as specified,
carry out the following tests:


Check vacuum hose for cracks and other
damage.

Test vacuum hose for blockages at intake
manifold. To do this, disconnect hose at fuel
pressure regulator and blow into it.

- If there are no leaks and no blockages in the
vacuum hose, install new fuel pressure
regulator.

- Replace hose clamp that secures vacuum hose
to the fuel pressure regulator and make sure
that new clamp is properly installed.

Checking residual fuel pressure

- Residual pressure 10 minutes after switching off
engine (minimum pressure)

With engine cold: at least 2.2 bar
Pa
ge 41 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
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11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1

24-39

Fuel injectors, checking


A - Electrical testing of fuel injectors

- Disconnect harness connector from injector to
be tested.

Note:
When the engine is at operating temperature the electrical resistance of
the injectors will be about 4 - 6 . higher.
If the specification is not obtained: - Connect hand-held multimeter to fuel injector (resistance measurement
range).

Specified value: 13.5 - 15.5 - Replace fuel injector Page 24
-53
. Also observe notes on Page
24
-51
.
Pa
ge 46 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
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11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
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e=re
pair&id=AUDI.B5.FU04.24.1

24-47

- Lift fuel rail off intake manifold together with fuel
injectors and support the fuel rail.

Note:

After lifting off the fuel rail, check to make sure
that the injectors are properly secured to the
fuel rail.
It is possible that some of the fuel injectors will
become detached from the fuel rail and remain
in the intake manifold when the fuel rail is
removed. If this happens, install the fuel
injectors back onto the fuel rail Page 24
-53
.

WARNING!
Make sure test box is inside of passenger compartment. - Connect test box VAG 1598/31 to wiring harness for engine control
unit. Do not connect to the engine control module itself Page 24
-20
.
Pa
ge 56 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1