what would cause a slight vibration at idle in gear,put it in neutral and it goes away?

does it matter if the car is warm cold has ben driven has not...hows your trans fluid..harmonic balancer any rotating parts..

I'd check you engine mounts

how much play should be in the rear mount,i put a pry bar on the mout and moved it.little play but it was not ripped,how many mounts are there?..3?

I'm not sure on the 00+ H-body. I check my mounts this way. Have a friend trans brake in forward and reverse and watch for excessive engine rocking.

Iac sensor under the throtele body clean and try before replaceing

x2

A bad IAC Sensor would not cause an engine vibration. It would cause a rough (bouncing) idle. Also, a bad or gummed up IAC sensor would cause that symptom regardless of whether or not you're in gear or neutral. The fact that he'* having this problem in gear and not in neutral is a telltale sign that his engine mounts are bad. When the car is in gear, the engine and transmission put a force on the engine mounts to pull the car forward. When in gear, that force isn't there anymore. If the engine mounts are bad, the engine'* vibration transfers to the car'* body instead of being absorbed.

I know the rear one is good,the rubber is not ripped at all,guess i will check the front one.