Lately 2000 F150 4.2 has been pi**ing me off, when running through the gears normally the rpm's hang while Im shifting and don't drop until I'm into the next gear... I've cleaned my MAF (although the truck isn't running rough), I cleaned my IAC and also swapped another IAC onto the truck, no difference...

Another thing I noticed is the rpm's hang longer when it is up to normal driving temp... anyone have any ideas???

 

sounds like a vacuum leak.

Robbie

 

I have no idea what else it could be, would a high Thottle position sensor voltage cause this as well? Or would that just cause high idle?

 

If you don't find any vacuum leaks, try replacing the tps.

 

It is a vac leak forsure, My TPS was stuck on damn good, I even stripped one of the screws But I have another 4.2 so I just swapped the Throttle body(s) and TPS, no difference.

I did tho clean my IAC again, only this time I forgot to plug it back in, fired up the truck... no surge to 2.5K on startup, no high idle and no hanging revs... so from what I've heard if your truck runs w/o the IAC plugged in then its a vac leak....

Any ideas on how to test and pinpoint a vac leak?

 

Yeah, I've heard of people spraying starting fluid around the vacuum hoses to pinpoint a leak. If your engine revs up after you spray it in a certain place, the leak is close by. Just be careful with the stuff, and don't spray it on anything hot like the exhaust manifolds, headers, etc. Good luck with it.

 

Uhhh. Mine's an 03 and I have a hanging rev thing, too. But it was like that when I got it (used, 50k on the OD)... Is this right for an 03, or do I, too have a vac leak?