I’m trying to get my daughters 03 Alero running properly again. I replaced the down stream 02 sensor and checke dthe fuel line pressure but the engine stutters whenit reaches 4000rpm’s and when the throttle is held steady at this speed the engine goes back and forth between 3500 and 400 rpm’s. Any idea what is causing this to happen?
It sounds like the rev limiter is engaging and preventing the engine from going higher than 4000 rpm. Almost all cars made since the mid 1990s, particularly domestic cars, have this feature. My 1996 Mercury Sable does it, as does my sister’s 2002 Pontiac Grand Am (same car as an Oldsmobile Alero) and my brother in law’s 2002 Pontiac Grand Prix. Take the car for a drive and try a full throttle acceleration run. I bet it will pass this test just fine. Another thing you could try is to put the transmission in neutral and try revving the engine. The rev limiter may allow more rpm’s when the transmission is not in park. Many domestics do, but I have never tried it in my sister’s car, so I couldn’t tell you if this is the case with your car.