Engine won't idle...HELP
 

Please help me...I'm frustrated.

My 1997 4.6L V8 (F150) has developed a weird problem. It will start just fine, but it does not want to run at idle...it will run if I give it a lot of gas. But as soon as I drop the RPM below about 1,000, the engine literally just shuts down as if I turned off the ignition (doesn't sputter or anything like that). There is no check engine light, the engine sounds normal while it's running at high RPMs, and ther are no other symptoms that are obvious.

The truck has 99,800 miles on it, and was sitting a lot for the last 7 months while I was out of town. My wife would start it every few days and let it run a few minutes, and she would drive it around about once a week.

This problem happened out-of-the-blue. Any ideas?

I'm not an expert, especially on the 4.6, but it sounds kinda like a vaccume leak to me.

Almost Positive it is the IAC (Idle Air Control) Valve. Although I don't have picture's of where the IAC is on the Ford 4.6 Liter Engine. Doing a search on this forum for IAC will bring up many results on the matter.

What happens is the engine will create carbon build up, and will clog up the IAC making not enough air to get into the engine, hence a rough idle; if any.

Happened to my truck at about 60,000 Miles. Oh, and it's usually an easy instal if you can find out exactly where it is (Which you should) and is about $40 at any Auto Parts Store.

Hope this helps

he's right its most likey to be the IAC because when your foot it not on the throttle the butterfly valve is closed and the only air getting in is through the IAC.
have fun

Fixed!
 

Thanks all to the replies!!! I checked all the vacuum hoses, and they seemed to be OK. So I went down to NAPA and picked up an IAC Sensor for $50 (they list them at $100, and usually sell them for about $70...but you gotta ask for discounts if you shop regularly). Anyway, put the sensor on and she started right up with no problems. The removal and installation were extremely easy on my 4.6L...two bolts, right on top. I wish everything were this easy. Took 10 minutes going slowly (the old gasket had a piece that needed to be scraped-off).

I guess I have been quite fortunate with my F150, as this is the first time this has happened, and I've owned it since it was new in 1997. This has been THE most trouble-free vehicle I've ever owned. Today was also the first time I've ever washed build-up off of the battery posts. While I'd like a new truck, it's hard to justify getting rid of a vehicle that has been trouble-free and still runs great at 99,800 miles.

Thanks again for making this a cheap, quick, and easy fix!