My engine (2.0 911T) is vibrating when I I�m accelerating
 

My engine (2.0 911T) is vibrating when I I�m accelerating and the engine dos not have as much power (It happen over night).

When I hit the throttle in natural gear, everything�s seams fine, but as sone as I set it in gear it is vibrating.

I might have had a little to much oil in the motor (but only a little to much)

What can it bee, the spark plugs?

Thanks for your help.