Surging idle problem

[fr50089]

This might have been covered a bunch and if so Im sorry just need some input. I have a 95 gt convertible and it is bone stock minus gears and shift kit. It runs great except when im come to a stop light or have it in park it surges up to about 1000-1100 rpms and back down. Could this just be my IAC needs cleaned or something else?

 

[99FiveOh]

The only fix for this is to jack up the license plate and replace the car with something other than a 94/95 Mustang...lol.. Seriously, I've been trying to figure this problem out for years, some cars do it while others don't.

 

[MackGerard]

My car does the same thing. When I first turn it on in my driveway occasionally it will rev up to 1500-2000 rpm's for 5 seconds, then go down to 1000 rpm's for a couple more seconds then back down to my idle of about 650 rpm's I've tried so much to fix it nothing worked. on YouTube there is a guy that fixes up a 95 cobra that has the same problem and if I remember correctly he put about $1000 into fixing it, replacing almost all the sensors, his fuel pump, some lines and a bunch more. Nothing fixed it then his friend just yanked out a sensor and it stopped.

 

[99FiveOh]

When you start it up in the morning it's supposed to rev up a little bit, that is normal.

I honestly think the problem lies within the air intake design. When I converted over to Fox throttle body way back when, my idle surge problem went away, and the car felt like it had more pep off the line as well.

 

[fr50089]

My surging happens after about 5 minutes of it being started up and the engine is warm im going to try cleaning some stuff like IAC and see if that fixes it and if it doesnt I will probably look into changing over the the fox throttle body (since I wanted to do that anyway) and see if that fixes it. It doesnt hurt the performance its just kind of annoying.

 

[JonezySN95]

Check all you vacuum lines. My boss has a 2000 saleen and it had the same problem (only when it was warmed up). It wound up being a very small vacuum leak.

 

[95Vert383AOD]

My 383 95 Mustang does this "SOMETIMES". Some days the idle is beautiful, other days the surging is so bad i nearly do a burnout at a red light holding the brake and keeping the car from stalling. My engine had been converted to the Fox setup. I think ill try brake cleaner in the IAC and then lubricating it with some wd40. Usually the IAC sticks rather than the motor failing.

Chris

 

[toyman]

If you look carefully at the IAC there is nothing to clean other than the chamber and protective bellows. The solenoid which opens and closes the by-pass is sealed unless the bellows has split. Also, the by-pass is only open or closed. There is no in between position. If the IAC is the cause and it may be, your best bet is to replace it.

 

[HISSIN50]

If the surge occurs while still rolling, it can be by design. If it happens while completely stopped, that's another issue.

If you can narrow it down to an exact temperature range, that can also help (the strategies change and the trim changes, especially as the car nears operating temp).