Hey guys,

I'm having high idle problems on my Stang....a few weeks ago my RPMs were between 800 and 1100. I've been working on the Stang the last 2 weeks, so I haven't been running the car as much. Now the RPMs are constantly around 1100 then they drop after being revving the engine.

Before I get 10...clean your IAC responses. Would replacing the throttle body and elbow help this.....along with the IAC? Also other than the Ford dealer does anyone sell new IAC units?

The reason I ask about the throttle body is so that I can start planning for a K&N FIPK and Accufab throttle body/elbow combo. Along with being told this is another induction area that gets clogged after 75K(I've got over 82K).

 

I guess to clarify: Since I'm gonna replace the throttle body anyways...I'd rather do that than clean it then replace it a month or so later.

Also this is when the engine is cold, and of course.....idling.

 

Matt, engines when cold generally idle higher untill they warm up. Its fairly common, and my guess is the temp in your area has dropped noticeably in the past couple of weeks/days. This is why you may be noticing it more now.

I dont think replacing any parts will help it honestly. Something easy to try would be unhook the negative battery cable from the battery, then hold your foot on the brake for about 30sec to discharge any juice stored in capacitors. Let it set unhooked for about 15min, then hook it back up. This should reset the ECU and it will have to relearn the car. That may help it out if you've changed any of the induction/exhaust.

Also check for vacuum leaks and make sure everything is hooked up good as far as hoses and electrical connections.

Oh if you do decide to clean your throttle body, make sure you use a throttle body cleaner spray on it. The butterfly plate has a teflon coating on it to help prevent buildup getting on there and disrupting the air intake flow. Regular carb cleaner may wear or remove that coating.

 

I'll clean the IAC then try the battery thing, and then go for a cruise tomorrow.

From what I've been hearing 700-800 is the proper idle for a 99+ GT where as mine was bouncing between 800-1100RPM. Until last week it was a steady 1100RPM.

I think that will help a lot because the car has been in my driveway for the last 2 wks(not a daily driver). I've started the car up every other day...just to make sure it's starting, but I haven't given it a good drive in a while.

 

mine does the same thing if you start it in cold temperatures...it idles around 1100 or so for about 4 minutes until it warms up a little and then it drops down to like 900 or so. so i dont think what you have described is anything out of the ordinary...but it wont hurt to clean out those parts anyway.

 

It's not really cold....especially in South Texas. However, today it started acting odd.

I started the car....let it sit a while...drove to the gas station to get a fill-up. Then drove around a little while on the highway, then stopped at a store. Afterwards like mentioned the idle was around 800-900 which is fairly normal.

Later when driving on the street, as I approached stop signs the idle dropped to the 500RPM point; right around where the car wanted to die.....then it bounced up to a higher RPM. Of course from that point on....I was giving it gas just so it wouldn't reach that below 500RPM point.

I wanted to check the battery thing and IAC, but it was raining today. So that killed those ideas.

 

hmm im not sure. i dont know if thats really out of the ordinary. it might have to do with the fact that you dont drive it all the time. when im at school i only get to drive my mustang if i come home on a weekend and many times it takes a little while of driving it to warm it up. like...at first its a little rough shifting to 2nd and 3rd and sometimes it seems a little rougher than usual. but its always back to normal after 10 minutes or so.

as far as the idle thing...mine has fluctuated like that at stoplights before. i dont know if it went all the way down to 500 rpms...but i think a lot of it has to do with if you have the a/c or heat on and that kind of stuff.

anyway i dont think there is anything terribly wrong with you car...but better to be safe than sorry.

 

I think the thing that's hardest is...this is my first American and my first V8.

My import has a steady idle, and to see the Stang's jump I guess is a concern. I guess the other concern is....since I'm the 2nd owner I don't know what it was like stock.

So I think like Scott said....resetting the ECU might help.