2001 buick century engine stumbling

[pikeandchester]

2001 buick century 3100 motor 84,000 miles. Car hesitates on acceleration above 20 mph and motor stumbles/misses at cruising speed when heavy load is encountered (any hill) and shifts out of overdrive. Intake manifold was replaced at 58,000 miles. fuel and air filter, spark plugs and wires replaced at 80,000 with no change. check engine light not on, hooked up to scanner,no codes. throttle position sensor reads from 0%-100% smoothly while in "review data" on scanner. any ideas what could be wrong would be greatly appreciated.

[JOHNBIGDOG]

HOLD BRAKES FIRMLY, put car in reverse, Floor it. Does it misfire? yes? I would suspect the coil pack(s), If you have a scan tool you could look at mode 6 and see which cylinder was misfiring and replace that specific coil. I would assume (cough) that this is worse hot?

Someone may be able to enlighten me, I think this car has 3 coils and one coil driver, right?

[Jeremy airjer W]

Dirty MAF sensor?

[pikeandchester]

you are correct,3 coils. while engine cool i pressed brake firmly while in reverse and put the gas pedal to the floor, ran smooth. repeated when engine was at normal operating temp and still ran well. sprayed maf sensor with maf cleaner, removed egr valve and sprayed it with carb and choke cleaner. i have ran 2 tanks of gas thru with injector cleaner. no change after any of this. it seems there is a dead spot when accelerating, if i get heavy into the throttle it runs smooth, does'nt seem to depend on engine temp. i do have a scanner that give live data but i can't find anything telling me if a coil is bad. Thank you for the replies everyone's ideas are appreciated

[pikeandchester]

catalytic converter was bad

[Jeremy airjer W]

its been a good day for cats. We had two in the shop today. One plugged and one inefficient. Show me the money!