I have a supercharged 04 Monte Carlo that recently started having problems, When in park it’ll idle at 600 RPMs and jump up to 1300 and back down to 400 almost killing the car. Headlights also dim and dash lights dim as well. Car is not throwing codes, however I recently replaced the iac valve, vacuum manifold and MAF sensor… im puzzled as to what is causing my problem. Any help please

 

What's your battery voltage like? The dimming lights lead me to think the alternator is starting to go. You can always pull that and go get it bench tested.

Some of the idle issues could be related to that, but also could be your fuel pressure. You'll need to get a gauge on that and see where your pressures are at.