Idle Air Control (IAC) Functional Test
(1 of 2)
441
BLU/WHT
IDLE AIR
442 BLU/BLK
CONTROL
(IAC) VALVE
443
444
GRN/WHT
GRN/BLK
CIRCUIT DESCRIPTION:
DIAGNOSTIC AIDS:
The ECM controls idle speed to a calculated, “de-
sired” RPM based on sensor inputs and actual en-
gine RPM, determined by the time between succes-
sive ignition reference pulses from the ignition
module. The ECM uses four circuits to move an Idle
Air Control (IAC) valve, which allows varying
amounts of air flow into the intake manifold, control-
ling idle speed.
Checkforvacuumleaks,unconnectedorbrittlevacu-
um hoses, cuts, etc. Examine manifold and throttle
body gaskets for proper seal. Check for cracked in-
take manifold/plenum. Check open, shorts, or poor
connections to IAC valve in CKTs 441, 442, 443 and
444.
An open, short, or poor connection in CKTs 441, 442,
443,
or 444 will result in improper idle control and
IMPORTANT: Improper IAC readings or improper
idle speed can result from other faults ie: flood-
ing VST, fouled spark plugs, bad sensors. These
items should be in proper working order to en-
sure correct diagnosis.
may cause improper idle.
An IAC valve which is stopped and cannot respond
to the ECM, a throttle stop screw which has been
tampered with, or a damaged throttle body or linkage
could cause improper idle.
TEST DESCRIPTION:
Number(s) below refer to circled number(s) on the
functional check chart.
1.
This step determines if the IAC valve is function-
ing properly.
2.
This step determines if the circuitry or the IAC
valve is faulty.
Index
5C-78 - ELECTRONIC FUEL INJECTION (MULTI-PORT AND THROTTLE BODY)
90-823224--2 796
| Categories | Mercury MerCruiser Manuals |
|---|---|
| Tags | Mercury MerCruiser 454 CID, Mercury MerCruiser 502 CID |
| Model Year | 1993, 1994, 1995, 1996, 1997 |
| Download File |
|
| Document File Type | |
| Copyright | Attribution Non-commercial |
(4 votes, average: 4.5 out of 5)
Marine readers have rated 1993 1997 Mercury-MerCruiser GM V8 454 CID 7.4L and 502 CID 8.2L Marine Engines Service Manual Number 16 4.5 out of 5.0 based on 4 product reviews. Hugely helpful service manual! Perfect. Thank you!
Manuals are all Important for Technician
This book is invaluable if you do your own repairs. Great book.
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