High idle on 4.6
 

Truck revs up on start ups and is idling a little high.Tried to search before posting but no luck.(poor wording i guess)Wouldn't 700rpm be normal idle?She revs up on start up cold or hot to about 2200 Just does not seem right.

I've been searching for a solution to this as well. My 03 Exp EB with the 4.6L revs up to about 1600rpm the first cold start of the day which is fine. The problem is when you start the truck after it's warm. It revs up to 2000rpm and then slowly comes down. I've taken off the IAC and cleaned but still the same. I've been looking for ways to possibly restricting the maximum air that passes throught the IAC to perhaps slow the idle down a bit. I also discovered a strange empty black plastic box in the rubber hose that goes from the intake snorkle to the IAC. I don't know what the purpose of this is. My 96 5.0L Explorer never reved so high on initial start or for that matter any car I've ever had. I've heard this complaint over and over but have never heard why or how to change it.

Well we need some darn help!I dont suppose the MAF could do this?Come on smart guys we need ya!appreciate ya!

Call the dealer and see if there is a reflash for the computer for this problem idel control is a common problem with the computer. Give it a try this is a fairly cheap fix and check the intake gaskets too.

Cleaning the IAC usually doesn't do much, or if it does, not for very long.

Sounds like the IAC is stuck open. They should only be $30-40 and easy to change.

The MAF in the 4.6 usually doesn't cause high idles (although I know of one '94 t-bird 4.6L that did). It usually causes mixture problems under load, not idle issues.

The "black box" in the hose for the IAC is probably a filter of some type or resonator. It doesn't "do" anything.

I would not "reflash" until something is REALLY wrong... I've heard of people getting reflashed and not having the same performance afterwards - never heard of anyone getting an improvement from it.

One other thing, my wife's '97 Cougar 4.6L I recently did a tuneup on (and later an entire intake manifold because it cracked).

I checked the throttle body, and found enough corrosion in the throttle body bore where the throttle plate is that the plate couldn't completely close while the actual air-flow was cut off from the corrosion.

I know it's supposed to be "coated" with something, I cleaned it out with Scotch-Brite, not giving a darn if the coating was coming off, because the corrosion had already taken care of that. Runs better now. But, it didn't have a high idle like you're complaining about, but it has only 22K miles on it. Yours could be much worse than mine.

Also, check for obvious throttle cable binding, where the throttle plate isn't closing all the way.

I had the reflash done on both my explorer and F-350 and had considerable gains in mpg and power plus smother shifting trani on both and on the explorer cured my idel problems. If the right person does the reflash you can gain alot. I am taking my 95 cougar in for a reflash in the spring as the tech asured me that he would be able to get more power and even quicker shifts out of it. Its worth a shot

Thanks gonna give it a good look!I should probably know this but what is a reflash?Is that something they do with the computer?

Yes. They hook up to the computer and upload new "software" or more accurately "firmware" to the car's computer.

Sometimes, they can pick and choose, and figure out a better running firmware than what you have. I was going on V10 experience with re-flashes. Usually didn't do anything and usually made it slower.

The rule "newer is better" is not always the case with re-flashes.

Thanks Krewat I thought that was it.I will investigate this thing before any reflashes I was hoping it was common little dirty sensor problem.appreciate ya!

Grant12,
I would agree that the TPS may be going bad but thought I would add this just in case....
A while back I removed the Throttle Body on my wife's Expy 4.6L. When I put everything back together I had a very high idle. It revved up to about 2200 RPM, then backed off after a minute and repeated. It kind of oscillated back and forth for a while before I shut it off. Upon inspection I found a vaccuum hose had been left disconnected on the passenger side of the TB. It was a large hose with a 90' elbow. I had missed it because when it came off it landed on a screw and looked like it was connected to the intake. Anyway, I reconnected that and it instantly fixed the problem. I will look at tit and tell you where the other end goes when I get home tonight.

appreciate ya!!:cool: