High idle/engine surging
 

Hey all, new member here with a recently acquired 2002 F150 5.4 Triton.

When I first got the truck, at operating temp it was idling between 1100 - 1300 and would surge higher when the defrost was on. Banged my head against the wall for a while then ended up changing the PCV valve. Problem solved, idle went down almost instantly (600 - 700) and the surge no longer bucks the truck forward.

The truck runs a little rough now that idle is down, shakes a bit and hesitates once in a while if I step on the gas.

My question: What would the possible side effects of this 1100 - 1300 idle for 2+ years (that the previous owner is aware of) do to a 5.4? Would that foul plugs, or anything else I should be aware of? I asked the previous owner and he said a technician checked it out for that high idle and said it was normal. I politely told him to find a new technician ;)

Typically a high idle is caused by a faulty or dirty IAC...but you did get it pretty much resolved with a new PCV...which was likely due to a vacuum leak that old one was having. IDK

Did you check the PCV line and elbow toward the firewall side, that elbow is a problematic leak point.

If you can ask the former owner (FO) when the sparkplugs were changed last that would be helpful...if they can't recall, then a fresh set would not hurt! go with Motorcraft plugs they do the best job. I doubt if the prolonged high idle did any real damage. Fouled the plugs...hmmm maybe. Kinda depends on how many miles were put on during that time. frame.

Thanks for the info, enriched. I'll have to check out the IAC and PCV line, thanks for the tip. He wasn't sure how long ago the plugs were replaced, thought maybe 30k miles ago and the truck has 107k total.

I'll probably just swap them out to be safe. The interesting part of that high idle is after shutting the engine off there would be an slow oil leak, and that leak has gone away since I changed the PCV valve. Guessing it was excess pressure due to the plugged valve, and oil found a way out?