Cavalier engine problems

My son purchase a used 98 Chevy Cavalier with HO 4 cylinder engine. It has 125000 mile and he is having nothing but problems. Great looking car he had it a month when it started to misfire, we replaced the plugs and coil packs spark plug wiring system. It ran great for a month, now we are having problems again. If the car is running under 1500 rpm’s it runs great. Push the accelerator any harder and it dies remove your foot from the accelerator and the engine will still run as long as you are under the 1500 rpm limit. It does the same thing in park. We are not finding any error codes. We have replaced the fuel pump after our GM mechanic told us to. $500.00 later the very same problem.

u could have a throttle position sensor problem. those don't always throw a code.

it could be a number of things it can be throttle sensor, egr valve, or fuel regualtor

all of those sensors always put out codes, wether the engine light stays on, or just comes on once and a while then shuts off.

I have the same problem but its just hard speed up any one want to help me out (change spark plugs helped alittle) i was wondering if its head gasket 94 cavalier

Fuel pressure regulator?

to me it sounds like a fuel pressure regulator or maybe even the fuel filter needs replaced

I would also have a look at the fuel filter. a clogged filter can starve the engine of fuel when it needs it the most. Although it should have been replaced when you did the pump