Question about 2004 Chevrolet Impala

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I had a code for a bad IAC. I installed according

I had a code for a bad IAC. I installed according to instruction and now the car doesn't idle until warmed up. Could the IAC be bad but not bring back the code

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  • wpassmore May 10, 2010

    Cleaning throttlebody and iac port was done but maybe not very well. I'll try again

  • wpassmore May 10, 2010

    I will try this fix, however, I don't want to keep changing parts until I get the right one. I know that the MAF affects how it runs, but other than the poor or no idle when cold or cool it runs fine. Thanks for the help



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Hi! The IAC (idle air control) cant be bad since you replaced it for a new one. But I do suspect a faulty MAF (mass air flow) sensor, It has big contribution on engine performance specially on the idling. This may not give you a code but since you described your problem clearly I would suggest that you replace the MAF, it may not die now but sooner or later it will. Hope this helps and have a good one!

Posted on May 10, 2010


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1994 ford escort wagon lx 4cyl standard won't idle, dies at stops. Had idle throttle sensor and throttle sensor replaced. Doesn't help even though when coded it said that was the problem. Help!

The DTC - diagnostic trouble code may have had the word IAC - idle air control etc.... that doesn't mean the valve is bad . The IAC has electrical circuits associated with it . There could be an open circuit , short to ground , short to power etc.... The Idle air control passage could be plugged . How To Fix Car That Idles Poorly Clean the IAC
Ford idle air control valve IAC test stalling problems

May 06, 2017 | Ford Cars & Trucks

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How to fix fault code P1507

Possible causes
- Faulty Idle Air Control (IAC) valve
- Idle Air Control (IAC) valve harness is open or shorted
- Idle Air Control (IAC) valve circuit poor electrical connection
What does this mean? Tech notes
The P1507 code means that the engine idle is out of factory specification. Sometimes the Idle Air Control (IAC) may have carbon built up. Disconnect the car battery, remove the valve, clean, re-install valve, and drive the vehicle for about 5 minutes with the headlights and A/C ON to get the idle relearned.
If the problem persist, the IAC valve may need to be replaced.

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Nov 22, 2015 | 2000 Ford Ranger SuperCab

1 Answer

Where is the IAC on my 2002 Toyota Echo?

The IAC is on the bottom of the throttle body and has a hole in the bottom of the throttle body that lets air into the IAC. YOu do not have to remove it, if you do remove it the throttle body would have to come off and a new gasket would be required. Usually spraying through with throttle body cleaner will clean the IAC so it functions properly.

About your P0505 faut code, The IAC (Idle Air Control) valve controls the idle speed of the engine. At idle the throttle plate is closed, of course. The IAC is computer controlled and allows only a certain amount of air around the throttle plate. This metered air controls the idle speed. The IAC has a "plunger" or "shutter" that moves to open or close the bypass air passageway. The more air the IAC allows around the throttle plate, the higher the idle. The PCM (Powertrain Control Module) uses the IAC valve to keep the idle speed correct with varying engine demands. Can be a three or four wire sensor depending on the model.
The PCM monitors voltages of the IAC circuits and if it detects an incorrect voltage on one or more of the IAC motor circuits it will set P0505. NOTE: Problems with the IAC would only be noticeable at idle or when throttle is closed.

Symptoms may include:MIL (Malfunction Indicator Lamp) illuminationEngine stalls and may not idle unless throttle is depressedIntermittently stalls when letting off the throttleEngine may idle too high

Potential causes of an P0505 code include:IAC motor connector is damaged (check connector and pins for damage, and moisture)One or more IAC circuits open or shorted to groundOne or more IAC circuits are shorted to voltageIAC has failedPCM has failed

Possible Solutions:This should be a fairly straightforward diagnosis. Start by clearing the fault codes. Then unplug the IAC and start the engine (This may cause other IAC codes to set. Just ignore them for now). If the P0505 code doesn't reset, replace the IAC. It is internally shorting one of the IAC circuits. If the code DOES return after unplugging the IAC and starting the engine, then you know it isn't the IAC motor. Visually check the wiring harness all the way back to the PCM. You may need to visually inspect the harness by removing all the insulation off the wires. It is possible that the wires could be shorting to eachother or to other wires in the harness.
If there are no wiring problems, and the code keeps returning with the IAC unplugged, you can check the PCM by removing the IAC wires from the PCM connector (or clipping the wires in a location where they can be repaired easily) and then start the engine (If you're not sure, don't do it. Take it to a qualified professional). Now if the code doesn't reset there is a problem with the wiring. Check for continuity on all the IAC wires. Any resistance points to a problem. Check for voltage on any(At this point there shouldn't be any voltages on the wires because they're clipped at one end and unplugged at the IAC). Repair as necessary. But if the P0505 code DOES reset after removing the IAC wires from the PCM connector(or clipping them), replace the PCM, there's a problem internally on the IAC control circuit.

Hope this helps.

Mar 28, 2012 | 2002 Toyota ECHO

1 Answer

Car dies on decel no codes

It would help to have the model, year and engine since different years use different sensors and output actuators. With no codes present, i would look at the IAC valve (idle air control) assuming your model has one. This valve serves two purposes. One is to control the idle, and the second is to act as whats known a dashpot on older vehicles. It keeps the idle slightly higher so the vehicle doesn't stall when decelerating.

The valve is located near the throttle body and is controlled by the vehicles computer. It's usually easy to install and normally fastened by two screws. The part cost could be from $40 - $200, again depending on the model.

The only surefire way to diagnose this would be to install a scan tool and monitor sensors and the IAC duty cycle commanded by the computer. Good luck, if you want to add some more info I may be able to help a bit more.

Apr 15, 2011 | Ford Freestyle Cars & Trucks

1 Answer


JUST to be safe, pull the 3 pin plug on the IAC while the engine is idling. Does the idle change (speed should increase or start to fluctuate)? If not, you've got another bad IAC or there's a problem with the wiring/PCM that's not permitting it to work properly.

The code indicates there is an problem with your Idle Air Control System. Most likely failure is that the IAC system failed. There is an 3 pin from the IAC. Remove it from IAC when your engine is idling.Check whether there is an idle speed change? IF it does not fluctuate then your IAC has gone bad,

Feb 11, 2011 | Honda Civic Cars & Trucks

1 Answer

The engine runs really well, until you bring the car to a stop. Then it dies. Sometimes it dies when moving. Just push the clutch pedal in and when the revs go down, it dies.

The two most likely possibilities are a vacuum leak, or a faulty Idle Air Control (IAC or IDAC) valve.

Inspect the vacuum hoses for cracks or tears. With the engine running, listen for any tell-tale hissing sounds. Make sure there are no leaks in the intake manifold area.

Check the IAC wiring and connector. Use a voltmeter to test its harness. Refer to a manual for the specs of the voltages on the connectors. Also test the IAC itself with an ohmmeter. Again, refer to the manual for the correct resistances across the leads. Another diagnostic is to remove the IAC entirely, leaving the intake open. If the engine idles ok with the IAC removed, this is a sign that the IAC is not opening at idle as it should.

Mar 17, 2010 | 1993 Honda Accord

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2005 honda accord stalls every time i stop

Hi there Your idle speed is controlled by a idle control value. You must firstly identify whether your PGM-FI ECU has a blinking code and what that code is. It might identify that the idle control value is playing-up. You will find the idle control value connected to the inlet manifold by way of vacuum hoses. It might be that the vacuum hose has dropped off or is broken - if that's the case, simply reconnect or replace the vacuum hose and your problem should be rectified. Best regards, Scottech.

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Idle problem

How much is the Idle Air control valve?

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