I swapped the 2.8 motor (automatic) out of my 87 firebird with a 2.8 out of an 89 camaro (5-speed). The motor out of the camaro had no flex plate so I just threw on the one from my car. Once I got everything back together the car vibrates like crazy. What do I need to do to fix this problem?

 

I'm not too familiar with the 2.8 but it sounds like you need an externally balanced flywheel. But since you used basically the same motor to swap it with, that might not even be the case. My next question would be does it vibrate while parked or driving or only on acceleration or deceleration?

 

it vibrates most noticeably when idling in park.

 

from what I can tell, in 1988 the engine was switched to an internally balanced unit. Thus, your flexplate is probably weighted and throwing the assembly off balance.

http://www.engine-parts.com/GMV6/history.html