Idle air control valve?

You may have a vacuum leak, get a can of spray Throttle body cleaner, spray the vac lines and maniflod area, when the idle changes, youve found the leak! You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs!
Idle control diagnostics:
IDLE AIR CONTROL SYSTEM DIAGNOSIS 1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK in appropriate SELF-DIAGNOSTICS article. Go to next step. 2. Set parking brake and block wheels. Turn A/C off. Start engine and let idle. Install scan tool and select SPECIAL FUNCTIONS. Select IAC SYSTEM TEST, and then RPM CONTROL. Using scan tool, command engine speed to 500 RPM. If actual engine RPM is within 100 RPM of scan tool display, go to next step. If actual engine RPM is not within 100 RPM of scan tool display, go to step 4. 3. Using scan tool, command engine speed to 1200 RPM. If actual engine RPM is within 100 RPM of scan tool display, check for a non-IAC system problem (i.e., vacuum leak, sticking throttle cable, fuel system lean or rich, throttle body, poor electrical connections, faulty PCV valve, A/C compressor circuits). If actual engine RPM is not within 100 RPM of scan tool display, go to step 5. 4. Check for vacuum leaks, sticking throttle plates, faulty PCV valve, or restriction in air induction system. If problem exists, go to step 20. If problem does not exist, go to step 6. 5. Check for obstruction or excessive carbon deposit in throttle body IAC passages. If problem exists, go to step 21. If problem does not exist, go to next step. 6. Turn ignition off. Disconnect IAC valve harness connector. Check for poor connection at IAC valve. If problem exists, go to step 19. If problem does not exist, go to next step. 7. Connect IAC Driver (J-37027-A) to IAC valve. Set parking brake and block wheels. Turn A/C off. Start engine and let idle. Install scan tool and monitor engine RPM. Using IAC driver, extend and retract IAC valve. If engine RPM decreases and increases as IAC valve is cycled, go to next step. If engine RPM does not decrease and increase as IAC valve is cycled, go to step 22. 8. If RPM changes smoothly with each flash of IAC valve cycle, go to next step. If RPM does not change smoothly with each flash of IAC valve cycle, go to step 22. 9. Install appropriate IAC node light onto IAC valve harness connector. Cycle IAC driver and observe lights. Both lights should cycle Green to Red, but never off as RPM changed over its range. If lights flash as specified, go to next step. If lights do not flash as specified, go to step 12. 10. Remove IAC driver from IAC valve. Using DVOM, measure resistance between IAC valve terminals "A" and "B". See Fig. 8 . Also, measure resistance between IAC valve terminals "C" and "D". If resistance is 40-80 ohms on both measurements, go to next step. If resistance is not 40-80 ohms on both measurements, go to step 22. 11. Using DVOM, measure resistance between IAC valve terminals "B" and "C". See Fig. 8 . Also, measure resistance between IAC valve terminals "A" and "D". If resistance is infinite on both measurements, check for a non-IAC system problem (i.e., vacuum leak, sticking throttle cable, fuel system lean or rich, throttle body, poor electrical connections, faulty PCV valve, A/C compressor circuits). If resistance is not infinite on both measurements, go to step 22. 12. Turn ignition off. Disconnect PCM harness connectors. Check for poor connections at PCM. If problem exists, go to step 19. If problem does not exist, go to next step. 13. Remove IAC node light. Check for an open in IAC driver circuits between IAC valve harness connector and PCM harness connector. If problem exists, go to step 19. If problem does not exist, go to next step. 14. Using a test light connected to battery voltage, probe IAC valve harness connector terminals. If test light illuminates at any terminal, go to step 17. If test light does not illuminate at any terminal, go to next step. 15. Turn ignition on with engine off. Using a test light connected to ground, probe IAC valve harness connector terminals. If test light illuminates at any terminal, go to step 18. If test light does not illuminate at any terminal, go to next step. 16. Check for a short between IAC valve circuits. If problem exists, go to step 19. If problem does not exist, go to step 23. 17. Repair short to ground in IAC circuit. After repairs, go to step 24. 18. Repair short to voltage in IAC circuit. After repairs, go to step 24. 19. Repair circuit as necessary. After repairs, go to step 24. 20. Repair condition as necessary. After repairs, go to step 24. 21. Clean IAC passages. After repairs, go to step 24. 22. Replace IAC valve. After repairs, go to step 24. 23. Replace PCM. Program PCM. Perform VTD password relearn procedure and crankshaft variation learn procedure. See COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION. After repairs, go to next step. 24. Install scan tool. Start engine and let idle. Turn off all accessories. Using scan tool, command engine speed to 1200 RPM, and then down to 500 RPM. Again, using scan tool, command engine speed as specified. If actual RPM is close to commanded RPM, system is okay. If actual RPM is not close to commanded RPM, go to step 2.
4/15/2010 ...

What I need to know is does yours have the accelerator cable? Or electronic gas pedal? If it's cable operated, remove the cable from the throttle body, and see if it idles normally. If it does, the cable might have a burr inside the guide. Replace cable. Does the plate close fully at idle? If not, it may need a new throttle body. And check for any PCV restriction.

About the scan tool, most generic scan tools cant do these particular tests, this is for GM Tech II scan tool. Check for wear inside the throttle plate area, and for in and out movement of the plate, it may need a new throttelbody, or possibly a new TPS. Could be sticking?

Cruise control would be my guess?

Try cleaning out the IACV and see what happens

Check for a bind in the cables to and from the cruise control unit.

Mickey-d

The common mistake is the diagnostic fault code did not say to replace the idle air control valve or that is was defective. Fault codes never say to replace parts. They only indicate the circuit or system that needs further diagnosis or the unacceptable operating condition. This valve has a very low failure rate, at least as far as electrical failures are concerned. You didn't list the mileage so I can't make any judgements related to that, but based on age, I'd start by checking the wiring for insulation that's rubbed through and a wire is grounding out, or possibly a corroded or stretched terminal in a connector. Your mechanic can also use a scanner to run the valve through its range of travel to evaluate its operation.

First you have to know the exact fault code number. There are about a dozen related to the idle air control valve, and they mean very different things. That system doesn't have anything to do with the evaporative emissions system. Also, that system, which is also referred to as the "vapor recovery" system, isn't monitored on '95 and older models, so while it could have a leak, that won't be detected by the Engine Computer and it won't set a fault code.

To find a leak in the vapor recovery system, you really need a smoke machine. That allows you to inject a white, non-toxic smoke at 2 pounds of pressure, then you can watch for where it sneaks out. Other than that you're limited to a visual inspection, and that is only good for real obvious problems. Most leaks in this system are way too small to see by eye.

For the idle air control valve circuit, I already mentioned checking for bare wires and corroded connector terminals. Beyond that the testing gets a little more involved. You can use an ohm meter to test the resistance of the wires and the motor that runs the idle air control valve, and I mentioned the scanner for running the motor through its paces to see if it responds properly. There really isn't anything you can do yourself when a scanner is required.

35 - Idle air control sensor circuit fault

As you can see, fault codes don't get real specific. To add to the confusion, the idle air control valve, (automatic idle speed motor), is not a sensor as the code implies. AND, ... It's not a motor as we normally think of one that spins. This unit has four wires and four internal electromagnetic coils. It doesn't have brushes like most motors do. The Engine Computer pulses the coils with varying voltages and polarity to set the armature to the desired position, and as it rotates slowly, it extends a valve that is on the end of a threaded shaft. As that armature turns, it extends or retracts the shaft and valve to vary how much of a controlled air leak is exposed. As it opens the passage to allow more air in, the computer lengthens the amount of time it holds the injectors open to allow more fuel in. That is how the computer adjusts idle speed and holds it steady.

Remember too that this valve only affects idle speed, and nothing else. If idle speed is too low, you just have to hold the accelerator pedal down 1/4". The engine may be hard to start if you don't do that, and it may tend to stall at stop signs.

Hello,

Ok, with that year most fuel related problems won't set a code.

I have come across this to many times and the people have checked and double check and still crossed wires.

If firing order is correct then next step would be to check or just replace the Injector Assembly. I say replace cause it is located under the intake.

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Here is the exploded veiw.