Need help diagnosing engine idle/ revving problem
 

Hi, guys I need a little help diagnosing a problem. I would like to have an idea what may be wrong before I take it to a shop. Any help is appreciated.

2005 F150 5.4L 56,000 (+/-)

For about 2 months now whenever I start the engine it revs up to about 1800RPM for maybe 1 to 2 minutes or until it warms up and then settles into a regular idle and runs smooth.

For the past two days the engine has developed an idling problem. The engine develops a loping idle and starts sputtering, almost as if it were about to cutoff. It makes the truck shake. The truck looks and sounds like I have a hot rod designed to run smooth at wot.

Any ideas? Also have not had the plugs changed, yet.

I would check the fuel filter and the plugs. Its about time for the plugs to be changed in mine as well. But have you tried running the truck at wot? Maybe there is a blockage in the fuel line and running wot might be able to help free it. Hope this helps a little bit! :thumbsup:

I would clean your IAC and throttle body then see how she runs.

Does it idle high after coming to a stop, and then slows to a rough idle? Any codes? I'd be looking at the PCV elbow behind the IAC on the intake manifold. They like to melt over time, and create a large vaccuum leak.

Thanks for the responses. I think I was unclear about my intentions. I have absolutely no mechanical aptitude, whatsoever. I plan on taking it to the dealer for repair, but I would like to have an idea as to what may be wrong as I have found most service advisors don't know what they're talking about.

Also, an update. She cutoff on me at an intersection - fired right back up but I now have a check engine warning light on.

EsoxShep - It does not rev when I stop only when cold starting. After coming to a stop it just begins to rough idle.

That does sound like a very dirty fuel filter. I believe there suppose to be changed every 9000 miles or so.

You prolly have lean codes PO171 PO174.

Hey guys, thanks for the responses. I figure I would post my findings in case someone else comes across the same symptoms.

My local dealership inspected it and called me back. The diagnosis:

1. Coil pack on cylinder #6 was bad.

2. Bad coil caused or lead to computer code error that caused the engine to run too rich. Leading to....

3. All of the spark plugs are fouled.

So... I will find out today if they were able to change out my plugs successfully ... or not. Luckily extended warranty will cover almost all of the work.:)

Damn!! That would make her run like chit - she was sick that's for sure. It might be a good idea to question a possible injector problem to them, since the plugs where fouled and the 05's had injector problems in the past. The Tech's most likely are aware of that problem if the trucks at the dealership, but it doesn't hurt to ask about it.