Mercury MerCruiser MCM 454 Mag MPI Service Manual page 684

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