Hopefully someone can point me in the right direction on this highly annoying idle problem I've been having with my 2000 Pontiac Grand Prix GT with the 3.8L engine. It's been going on for the past few years and haven't been able to find a solution to this. The idle will surge up and down a few hundred rpms both in and out of gear (but not as bad in gear), which it only happens when the motors warmed up at operating temp.
A few summers back I replaced a few parts that could be linked to this surging idle issue. I replaced both the lower and upper intake gaskets, along with a new Delphi upper intake plenum. I had some electrical issues as well, with my headlights shutting off at random times...which I fixed by replacing the ignition switch wiring harness (which was a junkyard part). I also had a check engine light for evap code (ended up being a disconnected evap line to fuel sending unit), which I tried replacing a few parts such as the charcoal canister and canister purge valve in the rear of the engine before giving in and bringing it to a mechanic. I remember not knowing for sure what evap line from the canister purge valve went where...the way I have it on now is the tube towards the firewall going to the rear of the intake plenum and the tube at the front of the purge valve going towards the egr valve system...Can anyone confirm that this is the correct routing setup for these evap lines??
I've already tried spraying brake cleaner around the lower and upper intake gaskets as well as all the vacuum lines around the engine, which didn't effect the idle at all. I replaced the pcv valve with a new ac delco pcv valve but to no avail. I cleaned the IAC valve, EGR valve pintle, the throttle body, and the MAF sensor. My question to all on here is what direction i should be looking now....could a junkyard ignition switch wiring harness cause problems with a surging idle?
