My 05 sunfire gets this crazy vibration. If I turn the A/C compressor off or shift in to neutral the vibration stops. When it started last time, I was slowing down to make a turn. Once I entered the parking lot, I cycled through the gears in my transmission and once I hit neutral the vibration stopped. As soon as I put it back into drive the vibration started right up. Next I turned the heat off so I could hear it better, and as soon as I did that the vibration stopped again. Turned the heat back on and the vibration returned. I cycled through the blower selections and the vibration was only present when the defroster (which uses the compressor) was on.

Anybody seen this before or have any ideas what's going on

Thanks in advance.

Almost sounds like engine mounts. I'm only saying this because when i installed my solid upper mount and lower mount the vibes really get crazy when the compressor turns on.

check the rubber in your mounts for cracks. I have an 05 sunfire as well and when i changed my mounts , my stock ones had a lot of cracks in the rubber. Mostly just the upper mount though.

I just did my motor mounts, They are a common problem with these cars, Upper motor mount is usually the first issue, Now I just had a tranny mount go, Now when I put into reverse I hear it click semi pop, Plus the motor leans to the left side its the tranny. I would look into those as well.

Good Luck.

I also have cracks in my tranny mount