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TROUBLE DIAGNOSES
p 5 6 F - I
DIAGNOSTIC PROCEDURE 5
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IDLE AIR CONTROL (IAC) SYSTEM.
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t
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No light, one or
Flashing light
more terminals.
each terminal.
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Check for
Check for
open or short
faulty IAC
to earth in
terminals.
circuit with
If ok, replace
no light.
IAC valve.
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Repair and retest.
Ensure diagnostic bridge removed.
Engine idling at normal operating temperature.
A/C off.
Record closed throttle idle rpm in "Park or
or Neutral':
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Ignition "off''.
Disconnect IAC valve.
Start engine. Note rpm in ParklNeutral.
NOTE:
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Check resistance across IAC coils. (Shoul
be more than 30 ohms between IAC
terminals opposite harness connector
terms. ''A" to "B" and "C" TO "D").
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When performing this test.
NO rpm increase.
further checks.
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Check for faulty ECM
terminals or IAC terminals.
Check for 12 volts on
ECM pins 25 and 50.
IF all ok replace ECM.
Steady light one
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Check:
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or more terminals.
For high idle sppeds check
auxiliary
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ensure that a standard low
Replace
1
IAC
valve.
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air valve
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pinch air hose to plenem.
~f rpm drops:
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Disconnect ECM.
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Check for 12 volts and ground for
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power testlight is used. Do not
use a "high-wattage" testlight,
as the ECM could be
damaged. A high wattage
testlight will either give
inaccurate
test
results,
damage the ECM, or both.
Ignition "on".
Check for short
to voltage on
circuits with
steady light.
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the electric heater element.
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Measure the heater resistance
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is in the range 30 to 50 ohms.
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Remove the auxillary air valve and
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check that the blade is closed
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before the valve cools down.
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A
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For vacuum leaks (causes fast idle speeds).
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1
T
A
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For sticking or binding throttle
,
( 1
1
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~ l f a g e
shah, cables or linkages.
Ignition "off".
Reconnect IAC valve.
Start engine.
Disconnect IAC valve.
Probe each IAC harness
connector with test light
to earth while switching
ignition on and off
continuously with engine
stopped.
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sparkplugs for being excessively
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worn, or mis-gapped.
Coolant sensor resistance.
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voltage.
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See Code 14.
Tps operation.
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For dirty or loose battery cables
or earth straps.
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Note rpm in Park or Neutral.
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ECM earth circuit terminals at the
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head bolts for being clean and tight.
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Does not return to idle
Rpm listed in first step.
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ParklNeutral switch operation.
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For high or low fuel pressure, or
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leaking injectors.
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,
AIC relay control circuit failure.
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Returns to idle rpm
recorded in first step.
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Generator output
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if under 10 volts,
NOTE: If IAC valve is removed from throttle body, then the learned offsets in the ECM
,
ECM will not command the IAC to move.
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No trouble found
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IAC ok.
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If idle problem
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exists. continue for
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must be cleared:
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Throttle body
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remove IAC and inspect
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Ignition off, connect diagnostic bridge.
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Run engine, switch ignition off and back on again when engine stops.
bore for foreign material or evidence
of IAC valve "Dragging" in the bore.
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Depress accelerator six (6) times, remove diagnostic bridge and switch ignition off.
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