Isuzu 1999 RODEO Workshop Manual page 723

6E1–96
RODEO X22SE 2.2L ENGINE DRIVEABILITY AND EMISSION
f Rich heated oxygen sensor signal (low air/fuel ratio) –
The idle speed will be too low. Tech 2 IAC counts will
usually be above 80. The system is obviously rich and
may exhibit black smoke in the exhaust.
f Tech 2 O2 voltage will be fixed at about 750 mV (0.75
V). Check for high fuel pressure, or a leaking or
sticking injector. A silicon–contaminated heated
oxygen sensor will show an O2 voltage slow to
respond on the Tech 2.
f Throttle body – Remove the IAC valve and inspect the
bore for foreign material.
f IAC valve electrical connections – IAC valve
connections should be carefully checked for proper
contact.
f PCV valve – An incorrect or faulty PCV valve may
result in an incorrect idle speed. Refer to Diagnosis,
Rough Idle, Stalling.
If intermittent poor driveability or idle symptoms are
resolved by disconnecting the IAC, carefully recheck
the connections and valve terminal resistance, or
replace the IAC.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart:
Step
1 1. Ignition OFF.
2. Connect the IAC motor analyzer J 39027–A to the
IAC valve.
3. Set the parking brake.
4. Block the wheels.
5. Turn the air conditioning OFF.
6. Idle the engine in Park (A/T) or Neutral (M/T).
7. Install the Tech 2. Display the RPM.
8. Use the IAC motor analyzer J 39027–A to extend
and retract the IAC valve.
9. The engine speed should decrease and increase as
the IAC is cycled.
Does the RPM change?
2 RPM should change smoothly with each flash of the
IAC motor analyzer J 39027–A light.
Does the RPM change within the range specified?
3 Check the IAC passages.
Are the IAC passages blocked?
4 Clear any obstruction from the IAC passages.
Is the action complete?
5 Replace the IAC. Refer to On–Vehicle Service, Idle Air
Control Valve.
Is the action complete?
Idle Air Control (IAC) System Check
Action
1. The IAC motor analyzer J 39027–A is used to
extend and retract the IAC valve. Valve movement
is verified by an engine speed change. If no change
in engine speed occurs, the valve can be resettled
when removed from the throttle body.
2. This step checks the quality of the IAC movement in
step 1. Between 700 revolutions per minute (RPM)
and about 1500 RPM, the engine speed should
change smoothly with each flash of the tester light
in both extend and retract. If the IAC valve is
retracted beyond the control range (about 1500
RPM), it may take many flashes to extend the IAC
valve before engine speed will begin to drop. This is
normal on certain engines. Fully extending the IAC
may cause engine stall. This may be normal.
6. Steps 1 and 2 verified the proper IAC valve
operation. This step checks the IAC circuits. Each
lamp on the noid light should flash red and green
while the IAC valve is cycled. While the sequence of
color is not important, if either light is OFF or does
not flash red and green, check the circuits for faults,
beginning with poor terminal contacts.
Value(s)
— Go to Step 2
700–1500
Go to Step 6
RPM
— Go to Step 4
— Verify repair
— Verify repair
Yes No
Go to Step 3
Go to Step 3
Go to Step 5
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