Help with HIGH IDLE (Page 1/1)
etoangel MAR 28, 10:35 AM
Hey y’all, just got a fiero (1984 2m4) and love it, drove it for 150 miles no problem but then it randomly shut off while I was driving and I had to push it into a parking lot. it still turned over and the tachometer reflects engine turn over but the oil temp gauge is pinnned to the highest temp. I dug around and I thought oil sensor might be the culprit went to fix it and then it worked. Now I have another issue to tackle: the high idle. At first I thought it was a Idle control valve issue so I bought a replacement and it did nothing. I pulled the icv and plugged the hole and idle was still super high so that tells me I have a huge vaccum leak. So I replaced all of the vaccum lines with new ones and there's still a crazy high idle (2500 rpms). I put the car in diagnostic mode and it appears that the ecm is not communicating with the icv properly because I don't hear any clicking and trying to re-teach the idle did nothing. I have a replacement MAP coming in (I don't think anything is wrong with this one but the part is cheap enough that it's not hard to replace) and I also have a PCV valve coming in because mine crapped the bed (and its a 2 dollar part).

Does anyone know of any other ways of checking if the ecm is communicating properly with the ICV? and/or checking if the ICV is working?

Should I just say F it and stick a plug in the icv valve and drive it that way? I really don't wanna mess up my transmission by slam-fking it into gear when it's at 1000 rpms.


Car info:

100k miles on the dot. not molested in any way (that I know of) Fuel is good and clean Oil is good full and clean Engine temp is fine and was the whole time I was driving.

Idles high when not in gear. Doesn’t really effect drivability, just annoying.

Wasn’t blowing hot air from climate control.

Any and all help is appreciated. I just wanna get back on the road. 😊

[This message has been edited by etoangel (edited 03-28-2025).]

Patrick MAR 28, 02:58 PM

quote
Originally posted by etoangel:

...the oil temp gauge is pinnned to the highest temp.



Oil temp gauge? Is this something aftermarket... or do you actually mean the oil pressure gauge?


quote
Originally posted by etoangel:

I dug around and I thought oil sensor might be the culprit went to fix it and then it worked.



Probably just a poor electrical contact then.


quote
Originally posted by etoangel:

I pulled the icv and plugged the hole and idle was still super high so that tells me I have a huge vaccum leak.



What hole exactly did you plug?

Is there a functional 195° thermostat installed?

What temperature is the CTS reporting to the ECU? (Not what the temperature gauge might be indicating.)
etoangel MAR 28, 03:27 PM

quote
Originally posted by Patrick:

What hole exactly did you plug?



The IAC hole


quote
Originally posted by Patrick:

Is there a functional 195° thermostat installed?

What temperature is the CTS reporting to the ECU? (Not what the temperature gauge might be indicating.)



I am not sure if the thermostat is functioning properly


quote
What temperature is the CTS reporting to the ECU?



Do you know how I can check this? ECM doesn't currently have any codes.
Patrick MAR 28, 04:05 PM

Plugging the same hole you removed the IAC valve from accomplishes nothing.

This recent thread will probably answer all of your questions - 2.5L high idle
steve308 MAR 28, 08:41 PM
Did you happen to pull / check for codes? If no, it could save you a lot of guessing.
etoangel MAR 28, 08:47 PM

quote
Originally posted by steve308:

Did you happen to pull / check for codes? If no, it could save you a lot of guessing.



No codes last I checked. After installing the new thermostat tomorrow I will try to pull some codes again.
etoangel MAR 29, 04:45 PM
Update, apparently there was no thermostat installed before. I installed a new one and a new PCV valve. The engine finally heats up past 100 but now if I sit and let the car idle (which the car still idles at around 2500 RPM) after about a minute, I get a check engine light. Gonna check what the check engine light is for and will update.