DIAGNOSTICS
SERVICE MANUAL NUMBER 24
Chart A-8 (1 of 2): Idle Air Control (IAC) Functional Test
ECM
MEFI 1
MEFI 3
MEFI 2
J2-28
J2-13
J2-14
J2-29
J1-28
J1-12
J1-11
J1-27
441
BRN OR BLU/WHT
442 RED OR BLU/BLK
YEL OR GRN/WHT
LT GRN/BLK
IDLE AIR
CONTROL
(IAC) VALVE
443
444
CIRCUIT DESCRIPTION:
The ECM controls idle speed to a calibrated “desired” rpm based on sensor inputs and
actual engine rpm. The ECM uses four (4) circuits to move the Idle Air Control (IAC) valve.
The movement of the IAC valve varies the amount of air flow bypassing the throttle plates.
The ECM controls idle speed by determining the position of the IAC valve.
DIAGNOSTIC AIDS:
An intermittent may be caused by a poor connection, rubbed through wire insulation or a
wire broken inside the insulation. Check for the following items:
•
•
Poor connection or damaged harness. Inspect the ECM harness and connectors for
improper mating, broken locks, improperly formed or damaged terminals, poor termi-
nal to wire connection, and damaged harness.
Check for vacuum leaks, disconnected or brittle vacuum hoses, cuts, etc. Examine
manifold and throttle body gaskets for proper seal. Check for cracked intake man-
ifold.
•
•
Check for poor connections, opens, or short to grounds in CKT’s 441, 442, 443, and
444.
This may result in improper idle control.
An IAC valve which is “frozen” and will not respond to the ECM, a throttle stop screw
which has been tampered with, or a damaged throttle body or linkage may cause
improper idle.
Index
Page 5G-44
90-861327--1 OCTOBER 1999
| Categories | Mercury MerCruiser Manuals |
|---|---|
| Tags | Mercury MerCruiser 305 CID, Mercury MerCruiser 350 CID |
| Model Year | 1998, 1999, 2000, 2001 |
| Download File |
|
| Document File Type | |
| Copyright | Attribution Non-commercial |
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