QuarterMileMaster

I have a 98 Cobra, stroked, freshly rebuilt engine with less than 800 miles on the engine. The car runs great. BUT... when I stop, the idle stays at about 1100 RPMs for 6-7 seconds before dropping down to 800 where it belongs. I don't know what could be causing this and it's really annoying me. The only thing that is remotely wrong with the car is that the exhaust is leaking at the flange connecting the headers to the h-pipe because I didn't have the gaskets at them time... but will be putting them on shortly. Could that cause this for some strange reason??

If not, what could it be? What should I check??

Thanks

chrismartintx

i am not sure if it could be from that but since you mention it... following my x-pipe install i was having this problem. not constantly but probably >50% of the time. i suspected i may have a leak. pulled the pipe down got another new gasket layed down a bead of rtv & haven't had it happen since. now thats only like 10 miles of driving so i don't think its enough to consider it cured but its at least in remission...

xander0561

its the IAC conroller. It happens to my car too. You could do the IAC mod and that will fix that problem.

cliffyk

The IAC is sticking, it's normal (de-energised) position is open which admits additional metered air = high idle. When the PCM wishes to reduce the idle speed it applies a variable duty square wave signal to the IAC and the IAC is supposed to close proportionally to the duty cycle of the signal. [/align][/align]If the IAC is sticking mechanically, or if its solenoid's core has become magnetically saturated (age does this) it responds slowly to the control signal. You can try cleaning it with TB cleaner (although Ford does not suggest or recommend this), however replacement might be required. [/align][/align]To be 100% sure that it's the IAC and nota PCM problem you need to observe the IAC control signal with an oscilloscope.A new IAC is $75 to $90 at your FLAPS--might be cheaper than finding a mechanic that knows how to test it and the PCM properly.[/align][/align]