HOW TO: Bad idle troubleshooting
by the great : mpg9999
I noticed a decent amount of people here have idle problems, so I have typed up the FSM trouble diagnostics for an unstable idle. Enjoy:
1. Check EGR control valve for sticking (stick your hand under it and see if its stuck).
2. Perform power balance test: When disconnecting each injector harness connector one at a time, is there any cylinder which does not produce a momentary engine speed drop? If not, go to step 6.
3. Check Injector: Remove distributor from engine (crank angle sensor harness connector should remain connected). Disconnect ignition wires. Turn ignition switch ON. (Do not start engine). When rotating distributor shaft slowly by hand, does each injector make a n operating sound?
4. Check Ignition spark: Disconnect ignition wire from spark plug. Connect a known good spark plug to the ignition wire. Place end of spark plug against a suitable ground and crank engine. Check for spark. If no spark, check your coil, power transistor, and their circuits.
5. Check Spark plugs: Remove the spark plugs and check for fouling, etc.
6. Check Fuel pressure: Release fuel pressure to zero (pull fuel pump fuse and let engine die). Install fuel pressure gauge and check fuel pressure (at idle, it should be about 36 psi).
7. Check O2 sensor: Set “Exhaust gas sensor monitor” in the self diagnostic mode II. Maintaining engine at 2,000 rpms under no load, check to make sure that the red led on the ECU or the check engine light goes on and off more tan 5 times during 10 seconds.
8. Check for Intake air leak: When pinching blow-by hose, does the engine speed rise? If so, search for a leak.
9. Check idle adj. Screw for clogging: Disconnect TPS harness. Can you set engine rpm at 750 plus or minus 50 rpms by turning the screw? If not, check for a clog.
10. Do a compression check.
One thing this left out is checking the IAA. I would defiantly try that too if you are having idle issues. To check it, disconnect the AAC valve harness. If your engine speed does not drop, you may have a problem with your AAC valve.
I hope this helps you guys.
-Mike
I noticed a decent amount of people here have idle problems, so I have typed up the FSM trouble diagnostics for an unstable idle. Enjoy:
1. Check EGR control valve for sticking (stick your hand under it and see if its stuck).
2. Perform power balance test: When disconnecting each injector harness connector one at a time, is there any cylinder which does not produce a momentary engine speed drop? If not, go to step 6.
3. Check Injector: Remove distributor from engine (crank angle sensor harness connector should remain connected). Disconnect ignition wires. Turn ignition switch ON. (Do not start engine). When rotating distributor shaft slowly by hand, does each injector make a n operating sound?
4. Check Ignition spark: Disconnect ignition wire from spark plug. Connect a known good spark plug to the ignition wire. Place end of spark plug against a suitable ground and crank engine. Check for spark. If no spark, check your coil, power transistor, and their circuits.
5. Check Spark plugs: Remove the spark plugs and check for fouling, etc.
6. Check Fuel pressure: Release fuel pressure to zero (pull fuel pump fuse and let engine die). Install fuel pressure gauge and check fuel pressure (at idle, it should be about 36 psi).
7. Check O2 sensor: Set “Exhaust gas sensor monitor” in the self diagnostic mode II. Maintaining engine at 2,000 rpms under no load, check to make sure that the red led on the ECU or the check engine light goes on and off more tan 5 times during 10 seconds.
8. Check for Intake air leak: When pinching blow-by hose, does the engine speed rise? If so, search for a leak.
9. Check idle adj. Screw for clogging: Disconnect TPS harness. Can you set engine rpm at 750 plus or minus 50 rpms by turning the screw? If not, check for a clog.
10. Do a compression check.
One thing this left out is checking the IAA. I would defiantly try that too if you are having idle issues. To check it, disconnect the AAC valve harness. If your engine speed does not drop, you may have a problem with your AAC valve.
I hope this helps you guys.
-Mike
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Originally Posted by P10onP 
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