Low idle 1999 5.4 f150 with no codes
 

The truck ran fine this morning and this afternoon I had trouble with the truck running at idle.

The idle is at about 450RPM in park. Runs smooth with no miss but if you bring the idle up and then let off quickly it stalls. Can stall while trying to idle at warm up also. Sometimes it will stall at a light but I think it is related to taking my foot off the pedal quickly.

There is no check engine light on and there are no codes.

I have 138K on the engine now. Both air & fuel filter were replaced about a month ago as well as the PCV valve.

Replaced the plugs at about 105K.

Replaced the MAF about two months ago. Had no noticeable conditions but the check engine light came on and I got codes.

Cleaned out the AIC valve around 4 years ago but had different conditions like stumbling while cruising at highway speeds and idle dropping when stopping at the light. The idle with the AIC vale problem always came back up to normal. *Just found my old post from 4 years ago and it seams I did have similar conditions but the truck threw a code back then. Maybe I need to get someone else to read for codes.

It's either a vacuum leak or it's a sluggish IAC valve.

I sprayed around with some starting fluid and the idle didn't jump up so It could be the AIC valve.

That trick rarely, if ever, works with modern computer-controlled engines.

Mine has done that on and off for years. If you have worked on it you know where the IAC valve is. I tap mine with the handle end of a big screwdriver and she idles right up and I'm good sometimes for months. I am so disgusted in the quality of replacement parts these days,that the original sporadic one that is almost 16 years old is probably better then a new one...maybe.

That's what it was alright. I lost a socket and short extension down between the intake runners and into the valley. I can forget about getting those back.