1994 Pontiac Grand Am engine problem

I went in and changed the catalytic converter with no help also. To give a little more information. After the car had been sitting all day, it started with no hesitation. It still had a bad miss, but it started and moved under it's own power. I noticed after about 10 minutes once the motor had warmed up that the miss got really bad and the car eventually stalled. It would only restart if I held the gas pedal to the floor and the miss and backfiring was terrible. Could this be a bad O2 sensor or something else?

Have also replaced the 02 sensor and the ignition coils and cleaned the injectors with no help. Could this be a timning issue?

I am having an almost identical problem with my 99 4 cyl. Grand am. It runs great for about 10 minutes, then crapola. Feel like it's running on 3 cylinders. Started as small hesitation at highway speeds under acceleration and got bad in about 3 weeks. Now always runs poorly. I replaced the fuel pressure regulator with no help for starters. Am still working at it and will let you know if I get mine fixed before you.

I have a 95 2.3 quad 4 also, I had a big knock, I changed the head, the timing chain and sprockets, then checked out the rod bearings, found those were bad, after the gm dealer had told me it was a bad valve. But I had a 93 toyota pick up 22R-E, it had the similar problem that u are having, I found that it was a head gasket problem, I replaced the head and gasket on the toyota engine, runs like a champ now