I PULLED A CODE OF THE COMPUTER PO300 RANDOM/MULTIPLE CYL MISFIRE DETECTED. CAR HAS 120K. SERVICE ENGINE LIGHT ON.
cly misfireing on 2001 Buick LeSabre
Get it fixed asap, could be leaking coolant in to engine through leaking upper intake manifold. Check your coolant level in overflow bottle and radiator (when cold) to verify. If it is a leaking intake could cause engine to hydrolock and more severe damage will result.
Check this out: http://repairpal.com/OBD-Code-P0300
I just had simular problem. Was the ignition control module. Runs great now. No misfiring.