Aspire/Festiva/Fiesta Possibly one of the original "sub compacts" this car offered amazinf fuel economy.

Fiesta idle problem

Old 09-05-2018, 04:05 PM
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Join Date: Sep 2018
Posts: 1
Default Fiesta idle problem

first post,

my wife has a 2011 fiesta that will erratically rev between 1k and 3k when at a stop. I pulled the codes and it was for mass air flow or cat failure. I changed the cat last year and it pasted emissions last week.

I took it it to the dealer and they sad it was a transmission control module and it was 3k to replace!!! ( replaced on warranty 2 years ago)

im a mechanic by trade but not a car mechanic, a transmission control module seems highly suspicious to me? I have had it changed already, and when it went bad the symptoms were completely different.

Has as anyone had this rev problem, and if so what was the fix.

thanks for any input!

Old 09-06-2018, 03:35 PM
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Join Date: Jun 2010
Posts: 9,254

There is an IAC (Idle Air Control)valve on the throttle body Most of the time idle control problems involve that valve. Not knowing how involved you want to get with it, it is always nice to prove to one's satisfaction that a part is defective before replacing it.
.If it malfunctions you might be able to see a signal variation and that could help with the proof, but wives don't give a hoot so you may resort to drastic measures and replace the IAC anyway. If you decide to go that route It would be a good idea to remove the negative batt cable and hold it against the pos cable end for a few minutes to erase some of the adaptive learning in the vehicle's computer. After replacing the valve and reinstalling the neg batt cable without touching the throttle pedal, start the engine and let it relearn the idle steps which it will do by itself. After about 5-10 minutes if idling take it for a ride and allow it to relearn your driving habits, it will.
Hopefully that should get rid of the problem,, hopefully !
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