2004 Pontiac Grand Am

Engine Performance problem
2004 Pontiac Grand Am 6 cyl Front Wheel Drive Automatic 84000 miles

recently had oil change at walmart(mistake) car started and ran fine before. After that it was hard to start and blew blue smoke. My mechanic put on diagnostic and reported two cylinders missfiring, changed plugs wire and fuel filters. No help.
tried other things with no results. While checking dipstick he noticed it was overfilled, drained a quart out, left car sit and tried restarting. Car now starts and runs fine.I told this to walmart manager and he said that overfilling would not cause that problem. What do you think
August 8, 2010.

Yes it most certanlity will overfilling would cause oil to push past rings fouling plugs. Also can cause major damage you got off lucky.

Aug 8, 2010.