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Hyundai iac won't open properly

Replaced IAC, car still will not idle properly. I disconnected IAC from engine, would idle very roughly.

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  • Cars & Trucks Master
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Check throttle position sensor.

Posted on Dec 03, 2012


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Posted on Jan 02, 2017

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Im having the same car has a idling goes up t0 3 on the rpm & then back down to 0?help anyone?

Posted on Oct 26, 2009

  • 61 Answers

SOURCE: 1999 Escort ZX2 idling rough & not shifting in to overdrive

This could be caused by several things. Bad MAF sensor, TPS could be defective. You need to have the vehicle scanned for codes. You can have this done for no charge at AutoZone.

Posted on Nov 18, 2009

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SOURCE: 2001 taurus dohc codes 171

There is a large vac line coming straight down from the throttle body that goes to the PCV system. See if it has a hole in it. It is likely sucking air.

Posted on Jul 17, 2010

  • 252 Answers

SOURCE: 1998 subaru rs impreza 2.5


Usually a vacuum leak will make the idle bog down rather than speed up, even if the ECU is compensating. It will be rough, but as you say, it's fine through the revs.

This leads me to think the PCV (postive crankcase valve) is not connected or is leaking. This raises the idle, although the ECU will suspect the IAC to be the problem. Check the PCV valve first.

Check the MAF sensor for dirt too.

Another point to make is the throttle body might be clogged/dirty. Get the intake manifold off again and clean it with petrol/carb cleaner and a toothbrush, check the condition of the rubber seals, if they are gunked up, the air speed will increase, causing a high idle. Check the exhaust manifolds for any build up/rust.

Finally, when were the O2 sensors last changed? If recently, are they the right way around? If not recently, try those, but make this the last resort as they can cost a lot.

I hope I have covered every eventuality as I can see how annoying this is for you. As you already mentioned, reset the ECu after each attempt.

Good luck, fire any questions back if you need.

Posted on Jul 18, 2010

  • 7 Answers

SOURCE: 2000 ford expedition ,,rough idle in park..rough

Check the fuel pressure at the rail assembly, there should be a min of 40 lbs at the rails. Do you have any loss of power under a load? You may have an issue with your o2 sensor that is causing the ecm to send an improper signal to the engine ign/fuel map.

Posted on Dec 07, 2010

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Related Questions:

1 Answer

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.

Read more:

Nov 22, 2015 | 2000 Ford Ranger SuperCab

1 Answer

1987 chevy r20 rough idle

Well, the computer is supposed to open the IAC to keep the RPM above 600 or so depending on the load on the engine.
If you have voltage and ground for the IAC it should raise idle speed to at least 1100 when you first start the engine cold.
If that is not happening, I would look for carbon build up in the throttle body. You can apply voltage to the IAC and open it to see if the air passage is open too.

Jul 25, 2012 | 1987 Chevrolet R20

1 Answer

Do I have a possible IAC valve problem?

I would say that is EXACTLY what it is! you've already "tested" it.
you could try cleaning it out. carb and choke cleaner works good

Jun 22, 2012 | Hyundai Cars & Trucks

1 Answer

Recurring low idle TC 0507 after replacing IAC (x3) full tune up(plugs and wires), coil pack and verifying all vacuum lines

Maybe check the connector to the IAC

Post #4:
"Great news, the car is FIXED! I had to break down and take it into a dealer because I was getting over my head with sensors and electrical mumbo jumbo. Also, I the car had two recalls out that needed to be taken care of.

At a total cost to me of $52.78 I now have a perfectly idling car. It turns out that the connector to the IAC was bad. The dealer didn't charge for the part, and they only charged the minimum cost for a diagnosis. I was sure going into it that I would be paying several hundred dollars for a new IAC and a few hours of labor, but that was not the case. I actually would deal with the Hyundai dealer here again, and I'm not a big fan of dealerships. Now the car runs great, and once I change the clutch this weekend, she will be running good as new. "

Jun 12, 2012 | 2003 Hyundai Elantra GLS

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

3 Answers

What causes 2000 taurus engine rough idle but no codes

remove neg. cable from battery so the ECM will reset this may work. make sure the IAC is air tight. if this doen't fix your problem have someone check the IAC valve if it's bad the part runs $300.00 pluse

Nov 25, 2011 | 2000 Ford Taurus

2 Answers


This is only a guess, because rough idle can be due to an infinity of reasons. On the Focus, assuming that the spark plugs and wires are all good (check that the wires are seated securely), then very often this is due to a problem with the vacuum lines or the Idle Air Control (IAC) valve. With the engine running, listen closely for any tell-tale hissing sound and try to locate it. Check that the vacuum hoses are all in good condition and that they are securely in place. The IAC is a little more complicated to check. Its job is to let air in when the throttle is closed. If it is not opening as it should then the engine will idle rough. One thing you can try is to remove the IAC entirely, leaving an opening for air to get into the intake manifold. If the engine idles better with the IAC removed, you will know that the IAC has a problem. It could be a problem with the IAC itself or with its circuit. Good luck, if you have any more questions let me know.

Mar 29, 2010 | 2001 Ford Focus

1 Answer

I have a 2001 Elantra with 68000 mi. It started to idle rough and when you put it in gear it also runs rough, but when I increase the RPm the roughness goes away. None of the dash lights are on and the...

Possibly it's the Idle Air Control (IAC) valve. It is attached to the intake manifold. It's supposed to open and let air in when the the throttle is closed. The simplest way to test it on this car is to remove it entirely. It is just held on to the intake manifold by a few screws, and removing it leaves an opening in the manifold to let air in. If the car idles smoothly with the IAC removed, you'll know there is a problem either with the IAC itself or with its circuit. You can test the IAC with an ohmmeter between the center prong and the two side prongs. Neither one should be an open circuit. You can test the circuit with a voltmeter on the harness, between the center slot and the two side slots. You can refer to for the complete details, available free with registration. Possibly it is clogged and you may just need to clean the IAC with throttle/carb cleaner. Let me know if this helps.

Mar 22, 2010 | 2001 Hyundai Elantra

2 Answers

Car stalls when you let off the gas when warm or idling

sounds like your IAC (idle air control valve) located on the throttle body towards the front of the engine held in by 2 torx screws. the iac controls the idle if the car when your not on the gas. i will post the steps to clean the iac and the passages that the iac goes into.

1. disconnect the iac connector
2. remove the iac
3 clean the iac pintle valve and check for wear
4. clean the passages that the pintle valve sits in (usually carbon build-up in there, you may need to remove the air intake tube and air filter box to get to the passages in the throttlebody)
5. if the iac looks ok and the passages are cleaned re-install and put everything back
6. start car and see if it idles like normal when warmed up. you may need to give it a few tries for the iac to re-learn its proper position so give it a few warmup cycles
7. if it still stalls check for proper operation of the iac via ohming out the connectors (if you look it up on google you will find the specs at which the iac is supposed to operate)
8. if the iac is working properly, check for vacuum leaks on the intake manifold and vacuum lines.
9. if no vacuum leaks are present and the iac id working properly after cleaning have a shop check the ecm (engine control module) for a bad circuit board, i've seen that haoppen as well

hope this helps!

Feb 16, 2009 | 2000 Pontiac Grand Am GT

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