I get a bouncing idle when shifter is in neutral or clutch pedal is down. When A/C is on it is not as prevalent or doesn't do it at all. Only happens after engine has gotten to normal operating temps. Buddy of mine suggested it might be the throttle position sensor. I just had the throttle body replaced about 4k miles ago. It did not do it right after the TB was replaced, so I don't think it is the TB unless it had an early failure. I suppose it could be a TPS. I see the numbers constantly fluctuating in my scanner for the TPS, but I think that might be due to the idle dropping below 800 rpm. Before I take it in to get looked at I thought I'd run it by the members here and see if anyone has experienced it. I did a search and I didn't see anything like what I'm experiencing.

I do not get CEL and the car never dies, just bounces the idle off the low end limiter when the rpms drop below 800. Of course if I apply a tiny bit of throttle it idles fine or if the A/C is on. That is about all the info I know at this point. Other than that the car runs fine.

2008 SS 80k miles.

 

Could be buildup on the valves, maybe an inspection of the intake and having the intake manifold removed would give some clue.