I recently bought a 2001 Cavalier from an auction for just over $2000. It needed some work, driver's side door wouldn't open, trunk wouldn't open and was sitting incorrectly. On the drive home I noticed the car behaving very sluggishly in terms of power. Like it had 50HP. Not knowing how much maintenance the previous owner did on the car, I did usual tune-up work. New spark plugs (BOSCH Platinum +4), new air filter, new fuel filter, oil change (Pennzoil 5W-30 Full Synthetic). For some extremely stupid reason, cylinders 1 and 4 had AC Delco plugs, and 2 and 3 had some cheap BOSCH plugs. Not to metion they had rust piled in the head around them, so I had to air blast it all out with an air compressor to be able to fit my socket on them. The Check Engine light was on too. Scanning the OBD, the car had threw a code for the catalytic converter, and another for the O2 sensor. I reset the codes and have driven it around for a few days. After a few days driving, the car has gotten steadily worse. The car isn't throwing any codes and the readiness monitor isn't complete. The car steady loses power the longer it is driven. Just starting it for the first time of the day, it will hit about 25 MPH in first gear before nearing redline, 40 in second gear, and so on. Slowly, performance degrades, the car only hitting about 17 in first gear before refusing to accelerate anymore, second gear being slower aswell. The car has adequate power from pressing the gas 15 - 40% of the way, 40%+ the car actually goes SLOWER. I can barely make it up a hill in 4th or 3rd gear going 45MPH, and it will refuse to hit 60 in 5th. The car is also getting absolutely horrible gas mileage, no where near the 30+MPG you would expect from a 4 cylinder.
I had reason to believe it was the fuel pump, but performance would be bad from start up, not degrade over time. The engine doesn't overheat, but when it gets warmed up is usually when it starts acting up. The lack of OBD-II codes leads me to believe the car's ECU has failed. I KNOW this car should not perform like this, I see videos on youtube of stock Cavalier's hitting the 108MPH speed limiter with ease, mine can barely tackle 65 on a good day.
I really have no idea what it is, and I would like to confirm if its the ECU before I spend 120 bucks on one.
Car: 2001 Chevy Cavalier Base, 5 Speed Manual, 2.2L.
Note: A/C On/Off has no effect on this.