[bigwave]

OK, wizzards this is the second time I've posted this one here and so far I've not solved my problem. My 1999 cobra conv. runs well and is mostly stock with the exception of a CAI, high flow cats, and high flow exhaust from cats back, it's a Magnaflow setup. It does the normal idle at start-up, around 1100-1220 rpms until warmed a bit then settles down to 750 just as it should. Now here's the kicker, after a little driving the idle creeps up to 1800~ then as high at 2400~ very annoying. It's seems to be worse with the 90+ degree weather we've been having. I've checked the system for air leaks and all looks good, looks VERY good infact. I've taken out the MAF and cleaned with break cleaner, I've unhooked the battery to reset computer two or three times, I've set my tune with my SCT tuner back to stock.
What else? No engine knock going on, car is runny well.

 

[schmitty426]

im no wizzard but my car is in the shop as we speek for that same matter just idleing at 3800 yes quite annying my guess is your idle motor is sticking at the higher rpm's my best advise is to get it fixed asap because sooner or later that idle will sart as high as your saying when u start the car and when u put it in gear it will drop down to normal but its going to perform a nutural drop and thats not a healthy thing to do on a tranny:nono:

 

[2Manystangs]

possibly it's the throttle body or linkage hanging up, also this can be addressed with custom tune

 

[bigwave]

I am going to change the idle-air-control valve tonight and see what happens.

im no wizzard but my car is in the shop as we speek for that same matter just idleing at 3800 yes quite annying my guess is your idle motor is sticking at the higher rpm's my best advise is to get it fixed asap because sooner or later that idle will sart as high as your saying when u start the car and when u put it in gear it will drop down to normal but its going to perform a nutural drop and thats not a healthy thing to do on a tranny:nono:

 

[bigwave]

Much, much, better

Replaced the IAC last night, took me about two beers and ten minutes (it was very hot and I was thirsty). MUCH better, idle settles down in an instant now, still a little high (1000-1100) but I've not yet reset the ECM. And it only stays at the 1000 mark for a few seconds then drops down to 750 where it should be. Bottom line I can now drive anywhere again with-out sitting at a stop sign and it revving up to 2500rpms for no reason. Before it only took until car was up to normal operating temp and it would start it's revving, me and my wife drove around last night for over an hour and never a hiccup :nogrinner:gringreen. New part was around $55.00 labor was two beers, that I would have drunk anyway, probably more if it hadn't fixed the problem.:winks

I am going to change the idle-air-control valve tonight and see what happens.

 

[Brutal Metal]

glad you solved it, when I saw the thread I was gonna say IAC!

 

[bigwave]

Sooooo much nicer

Yep, I just fired it up and drove it back to work from lunch; idle drops instantly to 1000~ then right down to 700-800 after a few seconds. It seems like it's dropping down quicker then last night, I assume the computer is re-learning a bit.

 

[Brutal Metal]

sometimes you can spray the IAC with TB cleaner and get them to work again but for $50 it's piece of mind cause high idles can be Annoying!

 

[bigwave]

Dirty IAC

I considered cleaning it, but on inspection it was OEM, so 11 years old, and looking on the inside and comparing it to the new one I had in my hand it was very dirty. I think they normally run around $79 bucks but the motorcraft store sold it to me for their cost.:bigthumbsup

sometimes you can spray the IAC with TB cleaner and get them to work again but for $50 it's piece of mind cause high idles can be Annoying!

 

[Snakebite01]

glad you solved it, when I saw the thread I was gonna say IAC!

+1 to that.. it's a very common problem and i always replace in everytime i buy a new stang just so i don't have to worry about it!!
a worry free mind is a clear thinking mind