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Can a IAC valve become bad without any showing any fault codes?

Tiny
MARK87
  • MEMBER
  • 2010 HYUNDAI I20
  • 1.4L
  • 4 CYL
  • 2WD
  • MANUAL
  • 60,000 MILES
When I put the A/C on the car engine shake little bit, different idle sound, from the Hyundai agency they mention the IAC valve need immediate attention that is to replace the valve. Since there was no stock of the spare the owner couldn't replace it. As I friend I remove the IAC valve for cleaning.
Put new gasket, there was some carbon deposit. The car run smooth for few days and again it came back the engine shake.

I put the scanner there was no fault code found nor pending.

Question is, can a IAC valve become bad without any fault code present? Should I remove the throttle body and clean as well?How to confirm the IAC valve itself which is faulty?
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Wednesday, January 13th, 2021 AT 5:28 AM

1 Reply

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
In short yes it can fail with no other indicators other then the vehicle will not run when idling. More then likely the shaking with the A/C on is not the IAC valve. When an IAC valve fails it may not cause any codes but the engine will not get enough air when idling so the engine will shut off.

There are no real tests other then to test the resistance of the valve but I would just replace it if it is suspect.

https://www.2carpros.com/articles/how-to-replace-an-idle-speed-control-motor-iac

However, the shaking when the A/C is on is most likely normal. Is this something that was just noticed or did it just start or even get worse? If this was not there and it just started one day, it may be an issue with the compressor. Clearly if there is no issue when the A/C is off, then the engine is running properly but when the additional load from the A/C is added it causes this vibration.

If it were me and it is not too bad then I would not worry about it right now and then keep an eye on it and if it gets worse then take action. Let me know what questions you have.
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Wednesday, January 13th, 2021 AT 6:41 PM

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