1991 ACURA NSX Service Repair Manual

(From page 11 -44)
Inspect the IG COIL (30 A) fuse

in the engine compartment

fuse/relay box.
Is the fuse OK?

Turn the ignition switch ON.
Disconnect the 3P connector of
each sensor one at a time: MAP sensor

EGR
valve
lift
sensor
Accelerator pedal angle sensor
Does the MIL remain ON?
Connect the service check con-

nector terminals with a jumper

wire.
Disconnect the 3P connector of

each sensor one at a time:
TP sensor
Ignition timing adjuster

Does the MIL indicate
code 7 or 18?

Turn the ignition switch OFF.
Remove the jumper wire from the
service check connector.
Connect the test harness.

Disconnect the "D" connector

from the ECM only, not the engine

wire harness (see page 11-37).

Check for continuity between

body ground and the following

terminals: D19, D20.

(To page 11-46) Replace the fuse.
Substitute a known-good ECM
and recheck. If symptom/indica-
tion goes away, replace the origi-
nal
ECM.
Replace the sensor that caused
the light to go out upon its discon- nection.
Replace the TP sensor or ignition
timing adjuster. (From page 11-44)

Turn the ignition switch
OFF.

Disconnect "A" con-
nector from the ECM.

Turn the ignition switch

ON.
Is the MIL on?

Repair short to body
ground in BLU wire be-

tween the ECM (A13)
and
MIL.

Continuity?

(cont'd)ProCarManuals.com

PGM-FI System
Troubleshooting Flowchart Engine Control Module (ECM) (cont'd)
(From page 11-45)

Is there continuity?

Reconnect all the connectors. Reconnect the "D" connector to

the
ECM.

Turn the ignition switch ON.

Measure voltage between body

ground and the following termi-

nals individually:
A26,
B2.

Is there less than 1.0 V?
Measure voltage between A26
(-) and the following: C1 (+) and

A25 ( + ).

Is there battery voltage?

Substitute a known-good ECM
and recheck. If symptom/indica-
tion goes away, replace the origi-

nal
ECM. Repair short to body ground in
YEL/WHT wire between ECM
(D19) and MAP sensor.
Repair short to body ground in
YEL/WHT wire between ECM
(O20) and TP sensor. EGR
valve life sensor, ignition tim-
ing adjuster or accelerator pe-
dal angle sensor.
Repair open in BRN/BLK (A26) or
BRN/WHT (B2) and G101 (locat-
ed at right middle of engine).
Repair open in YEL/BLK wire
between ECM (A25. CD and
PGM-FI main relay.
Check PGM-FI main relay and
wiring connectors at PGM-FI
main relay.ProCarManuals.com

Idle Control System

System Troubleshooting Guide

NOTE:
Across each row in the chart, the sub-systems that could be sources of a symptom are ranked in the order they should
be inspected, starting with . Find the symptom in the left column, read across to the most likely source, then refer to

the page listed at the top of that column. If inspection shows the system is OK, try the next system , etc.

If the idle speed is out of specification and the Malfunction Indicator Lamp (MIL) does not blink code 14, go to inspec-

tion described on page 11-88.

PAGE
SUB-SYSTEM

SYMPTOM
DIFFICULT TO START
ENGINE WHEN COLD
WHEN COLD FAST IDLE OUT OF
SPEC
(1,000-2,000
rpm)
ROUGH IDLE
WHEN WARM RPM TOO HIGH
Idle speed is

below specified
rpm (no load)
Idle speed does
not increase after
initial start up.

WHEN WARM
RPM

TOO LOW
On models with

A/T, the idle

speed drops in gear

Idle speeds drops

when air

conditioner in ON or

OFF

Idle speed

fluctuates with

electrical load
WHILE
WARMING UP

FREQUENT
STALLING

AFTER
WARMING UP
FAILS EMISSION TEST
IDLE

ADJUST-

ING

SCREW
IDLE AIR

CONTROL
VALVE
AIR

CONDI-

TIONING
SIGNAL
ALTER-

NATOR
FR

SIGNAL
NEUTRAL

SWITCH

SIGNAL
(M/T)
STARTER

SWITCH
SIGNAL
FAST

IDLE

THERMO
VALVE
HOSES

AND

CONNEC-
TIONS

CLUTCH

SWITCH

SIGNAL
(M/T)

AUTOMATIC

TRANSAXLE
GEAR

POSITION
SIGNAL

102

88

90

92


94

96

98


100


101ProCarManuals.com

System Description

The idle speed of the engine is controlled by the Idle Air Control (IAC) valve.

The valve changes the amount of air bypassing into the intake manifold in response to electric current controlled by the

ECM.

When the IAC valve is activated, the valve opens to maintain the proper idle speed.

(cont'd)
IDLE

ADJUSTING

SCREW

FAST

IDLE

THERMO

VALVE
IAC VALVE

TO PGM-FI MAIN

RELAY
YEL/BLK
BLU/REDProCarManuals.com

1. When the idle speed is out of specification and the Malfunction Indicator Lamp (MIL) does not blink code 14, check

the following items:
Adjust the idle speed (see page 11-102)
Air conditioning signal (see page 11 -90)
ALT FR signal (see page 11-92)
A/T gear position switch signal (see page 11-94)Neutral switch signal (M/T) (see page 11-96)
Clutch switch signal (M/T) (see page 11-98)
Starter switch signal (see page 11-100)Fast idle thermo valve (see page 11-101)
Hoses and connections
IAC valve and its mounting O-rings
2. If the above items are normal, substitute a known-good IAC valve and readjust the idle speed (see page 11-102). If the idle speed still cannot be adjusted to specification (and the MIL does not blink code 14) after IAC valve
replacement, substitute a known-good ECM and recheck. If symptom goes away, replace the original ECM.ProCarManuals.com

Idle Control System

Troubleshooting Flowchart
Air Conditioning Signal

This signals the ECM when there is a demand for cooling from the air conditioning system.

Inspection of Air Condition-

ing Signal.
Connect the test harness be-
tween the ECM and connector. Disconnect "C" connector from
the engine wire harness only, not
the ECM (see page 11-37).
Turn the ignition switch ON.
Measure voltage between C3 (+)

terminal and A26 (-) terminal.

Is there approx. 10 V?

Turn the ignition switch OFF.
Reconnect "C" connector to the
engine wire harness.

Turn the ignition switch ON.

Momentarily connect A15 ter-
minal to A26 terminal several

times.

Is there a clicking noise from the
A/C compressor clutch?

Start the engine.

Blower switch ON.
(To page 11-91) Repair open in RED/BLU wire be-
tween ECM (A15) and A/C
clutch relay. Is there a clicking noise from the
A/C compressor clutch?
Connect the RED/BLU terminal of
the 4P connector on the A/C
clutch relay to body ground. View from relay side
(sub relay box A)

RED/BLU

See air conditioner in-
spection (see section
22).
Substitute a known-
good ECM and re-
check. If prescribed
voltage is now avail-
able, replace the ori-
ginal ECM.ProCarManuals.com

(From page 11-90)
A/C switch ON.
Does A/C operate ?

Air conditioning signal is OK.
Is voltage less than 1.0 V?
Measure voltage between C3

( + ) terminal and A26 (-) ter-

minal.

Substitute a known-good ECM
and recheck. If symptom/indica-
tion goes away, replace the orig- inal ECM. Repair open in BLU/
BLK wire between ECM
(C3) and A/C switch.ProCarManuals.com