Check the cat and make sure it isn't plugged.
I bought a Regal (sorry) once with a blown motor and after test driving the new engine I put in, the ground glowed RED from the cat being plugged(obviously why the engine overheated).
A year later I power washed my SHO engine and unknowingly got some water into the spark plug recesses. On my way back from the powerwasher, the car ran like a two-stroke engine and later found out it blew my cat into pieces inside. Rattled alot, but no check engine light.
So, I guess my point is, check the cat to be sure...
