Idle issue

[GMan79]

I know, another idle issue post.

My 88GT idles up at start up and settles to 750 rpm when cold. Once I drive it and it warms up it surges to anywhere from 1200-1500 rpm and stays there until I put it into gear. With it running I disconnected the IAC and instead of it having trouble staying running and stalling it drops down to 750 rpm and idles fine. Any thoughts on what route to take to fix this issue?
Thanks

 

[General karthief]

Right off the top I would look for a vacuum leak.
Check for codes, look for lean codes.
DISCLAIMER: I am not a mechanic, I just can't afford to pay anybody to screw something up so I have to do it myself.
Oh, any modifications?

 

[GMan79]

Only mods are ported lower intake, headers and exhaust. I have to get a timing gun to set the timing and go from there.

 

[General karthief]

Only mods are ported lower intake, headers and exhaust. I have to get a timing gun to set the timing and go from there.

Did you move the distributor?

 

[GMan79]

I didn’t move the distributor. Last night I put marks at 10 and 14 on the harmonic balancer. I’ve watched several YouTube videos on setting the timing. Once I know the timing is right then I can do a base idle reset. Watched a couple videos about that as well.

 

[General karthief]

Have you checked out the 'Technical/How to' thread ?

Technical Thread/how-to Index

Guys, if "that should be a sticky," then please reply to this thread with the link to your suggestion and why you think it should be added. How to determine if a thread should be included: - Does the topic address a common fox 5.0 owner's needs? / Is it a frequently asked question? / Is it...

stangnet.com

 

[GMan79]

I haven’t, but I will now. Thanks

 

[Mustang5L5]

Dumo your codes (no check engine on '88) and perform a smoke test/check for vac leaks.

Those older speed density cars are VERY sensitive to vac leaks

 

[88VinoVert]

I know, another idle issue post.

My 88GT idles up at start up and settles to 750 rpm when cold. Once I drive it and it warms up it surges to anywhere from 1200-1500 rpm and stays there until I put it into gear. With it running I disconnected the IAC and instead of it having trouble staying running and stalling it drops down to 750 rpm and idles fine. Any thoughts on what route to take to fix this issue?
Thanks

Howdy,

My 88 LX was doing something similar. In my case, I just cleaned the IAC valve and throttle body with some throttle body cleaner and it started behaving. You may have already done this, just offering my path of least resistance solution. Good luck

 

[GMan79]

Well, I set the timing at 10. I’m in the process of doing a base idle reset and the initial TPS reading was 1.25. I can’t get the TPS reading to go below 1.1. I even drilled the openings for the screws so that I can adjust it more.

 

[AeroCoupe]

Pull the TPS off the throttle body and see if it will even go that low. May be that the TPS is shot.

 

[Mustang5L5]

1.1 is still acceptable.

Anything from 0.5v to 1.25 is acceptable. Outside that range you get a code 23/63. No code…carry on.


I have no idea what my tps voltage is. Never measured. I regular pull codes on my car and if I don’t have a tps code I don’t worry a second about it.

 

[General karthief]

Check how far the idle screw is turned in. You may need a base idle reset then check the tps.

 

[GMan79]

Well I think I did it! I got my tps to read .985. I had to elongate the holes for the 2 tps mounting screws. Once I did that I performed the base idle reset again and so far no idle issues. Let’s hope it stays that way for the foreseeable future. Thanks for all of the advice.