Engine Performance problem
1994 Mercury Marquis V8 Two Wheel Drive Automatic 124000 miles
My 1994 mercury grand marquis has a problem.
Before it occurred the car was running well and also has been taken good care of. Lately I've had a problem with the car. When i start the car the engine shakes slightly when running(like it needs a tune up) but i recently did a tune up(spark plugs, filters, & coil packs) and when i put it in drive(d) the car starts to idling up and down and when i accelerate the car stalls sometimes(mostly). Stalls & putters through all gears. Also the coolant, transmission & oil level is FINE. A mechanic took a quick look at it and said he think its the CATALYTIC CONVERTER. Please let me know what you think it is. If you need anymore info i will be happy to provide you with it.
THANKS IN ADVANCE