Hello all, I'm new to the site so please bear with me. As indicated above, I have a 1988 F150, 5.0L, fuel injected and it's idling way too high.

When I first start it up it idles at about 2100 RPM. I know it's going to idle high until it's warm, but that seems too high. Once it has warmed up it will idle at about 1100 RPM while in Neutral, which if I remember right is a little high. It seems like it used to idle at about 800 or 900 RPM once it warmed up, but I could be wrong.

The real problem is once it is in drive it idles at about 1600 RPM. It's to the point where if I am on a flat surface, put it in drive, and let it idle it will actually pick up enough speed it will shift into 2nd gear! Needless to say this is causing major problems while driving in the snow/ice!

Just wondering what I should check/do to correct this. I've read a few threads about the IAC valve, but it seems the symptoms of a faulty IAC valve are generally low idle speeds. Again, I could be wrong. Any help or additional information will be greatly appreciated.

Thanks
bigmac83

 

Check or replace your throttle position sensor, it's located under the TB. That's what it sounds like to me. To replace it you are going to have to take the TB off, so make sure you have a new gasket handy just in case the old one is no good when you take it off. Also make sure you have no vacuum leaks anywhere and also make sure your spout connector is plugged in to the distributor. Just some ideas.

 

I agree with franky, somewhat. I had a 5.0 that had a bad TPS, but it didn't idle high, it just didn't have much power. My high idle was caused by a vacuum leak at the upper intake manifold gasket. Mine was idling as high as yours is when I had that problem. It was at the back of the engine so it was hard to find. You have to take the throttle off anyway to get to that gasket so I would consider replacing the TPS while I was in there. Also check any vacuum lines coming off the manifold. Sometimes those get brittle and break. That's a pretty high idle for a little vacuum line, though. My bet is the gasket. Also try spraying some injector cleaner into the IAC, if it's sticking that might help it seat better.

 

Thanks for the ideas guys. Does anyone have any pointers on how to check the vaccum lines besides just looking at them? I think it could be more of a sensor issue because when it's in neutral with no load it idles fine, but as soon as I put it in drive it's off to the races. I didn't even think of the throttle position sensor. That seems like a good place to start.

I did check the IAC and it seemed like it was sliding freely. I did spray a little injector cleaner into it just for kicks and giggles, but it didn't seem to help.

Does anyone have any other ideas or suggestions. I'm open to just about anything!

Thanks again everyone for your help.

 

Welcome to FTE

Vacuum lines get brittle and crack, usually near where they connect. Very hard to see. I found the best way to check them is to just wiggle them a little. Generally the cracked ones will break right off.

IAC's need to be taken off and taken apart and sprayed with LOTS of TB cleaner to really clean them up. They get real sticky inside.

I'd agree that your problem is more toward a TPS being bad but have you pulled your codes to see what you have? Go here to see how if you don't have an OBD1 reader.

http://www.fordfuelinjection.com/?p=13

Good Luck
Bob

 

im having same issue what is a Iac unit

 

IAC = Idle Air Control valve.

 

tps is out of range....easy fix.....cheap too
change the tps...and you will be good to go