Engine hesitation, lurching, no power with acceleration, misfiring, sudden power

1995 Saturn SL2, DOHC, 109,000 mi. Will run ok when cold. After slight warmup and especially after full stop, car will not accelerate, missing badly, then slow movement under high rpms, then sudden lurching with power. Mechanic states fuel pressure is ok, and diagnostic code does not indicate O2 sensor. Diagnosed timing chain. Replaced timing chain and gears. But car still drives with all the same problems. Next mechanic claimed the problem is catalytic converter, then instead of replacing it he cleaned it out. Also put fuel ejector cleaner in the tank. Said things are really clogged. No effect. Car still has same problems but now getting worse and blowing some smoke which it did not before. I think it is the O2 sensor or the cat converter needs replaced. A friend suggested EGR problem. didn’t want to spend a fortune on this car. What is wrong?

have you put in new spark plugs ever? Take a look at the spark plugs one at a time and see what condtion they are in. This sounds a lot like plug fouling, and a rich mixture, which can be caused by a number of things, mostly sensors.

I have owned the car for 7,000 miles and have not check the spark plugs, but assumed the mechanic did check them. I’ll verify with him. No knowledge of the precious service history. Which sensors could be causing a rich mixture and should be checked out? Thanks for your help.

After verifying that the EGR valve is closed, disconnect it for a while and see if that improves things. Assuming your CEL is on, have the codes read and post them here…

Holy cow. What kind of mechanics are going to anyway? A timing chain? That one should be arrested or committed. A cat is possible but you can find out without all of the labor that you got charged.

What I think is that you should do all basic tune up items - spark plugs, wires, filters.

In addition - has anyone checked the coolant temp sensor? Someone should.