02 GP ,I had all of the engine mounts replaced and had a new GM cat converter put on about a year ago and ever since then at an idle in gear it has gradually developed a thumping noise which seems to be between the engine and firewall. Might be a coincidence that its done this since then but not sure? If I hold my left foot on the brake and just touch the gas with my right it stops. It sounds like something is hitting the firewall but nothing is. I have jacked the car up and tried finding it from the bottomside while running but the noise is not loud enough to be heard outside of the car. At times it seems loud enough to be heard from underneath but the closer I get to the area that I think its coming from I can no longer hear it because of engine noise.
Is it possible to turn the idle up a tad on these 3.8s or will that screw everything up? Also, what is the idle speed suspose to be on this car? Thanks
