1995 Mercury Mystique • 160,000 miles

I have a problem with my car vibrating at idle. Most of the vibration seems to be coming from the steering wheel. I replaces the front motor mount because it was cracked and the vibration is still there. I also got a tune up and that didnt help. The vibration seems worse at idle. The vibration occurs when idling in drive, reverse, neutral and park, although the vibration is less in park and neautral, it is the worst when in reverse. I was thinking that maybe the rear transmission mount needed to be replaced but cant get at it to see for sure. What would most likely be the problem?
February 12, 2013.

I would think a trans or motor mount. However, is the engine just running rough?