GENERAL SYSTEM DIAGNOSTICS
SERVICE MANUAL NUMBER 23
90-861326--1 MARCH 1999 Page 5E-91
Chart A-8 (2 of 2): Idle Air Control (IAC) Functional Test
Step Action Value(s) Yes No
1
Was the “On-Board Diagnostic”
(OBD) System Check
performed?
–
Go to Step
2
Go to OBD
System Check
2
1. Engine should be at normal
operating temperature.
2. Start engine and allow idle to
stabilize.
3. Record RPM.
4. Ignition “OFF” for 10
seconds.
5. Disconnect IAC harness con-
nector.
6. Restart engine and record
RPM.
Is RPM Higher Than The First
Recorded RPM By More Than
The Specified Value?
200 RPM
Go to Step
3 Go to Step
4
3
1. Reinstall IAC harness con-
nector.
2. Idle speed should gradually
return within 75 RPM of the
original recorded RPM within
30 seconds.
Does RPM Return To Original
Recorded RPM?
–
Go to Step
5 Go to Step
4
4
1. Ignition “OFF” for 10
seconds.
2. Disconnect IAC harness con-
nector.
3. Restart engine.
4. Using a test light connected
to ground, probe each one of
the four IAC harness termi-
nals.
Does The Test Light Blink On
All Four Terminals?
–
Go to Step
7 Go to Step
6
5 IAC circuit is functioning properly. – – –
6
Locate and repair poor
connection, open, or short to
ground in the IAC circuit that did
not blink. If a problem was found,
repair as necessary.
Was A Problem Found?
–
Go to OBD
System
Check
Go to Step
8
7
Check for poor IAC connections
or replace the faulty IAC valve.
Is Action Complete?
–
Go to OBD
System
Check
–
8
Repair faulty ECM connections
or replace faulty ECM.
Is Action Complete?
–
Go to OBD
System
Check
–
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