Engine Performance problem
1995 Pontiac Bonneville 6 cyl Front Wheel Drive Automatic 123k miles
My Bonneville will run fine but stumbles when going up a hill or during acceleration while cruising at highway speeds. If I go into passing gear it will smooth out. Sometimes it gets so bad the fuel pump in the gas tank hums pretty lowd (can be heard over the A/C & radio). I checked the fuel pressure and it was fine. The fuel pump was changed a few years ago and tune-ups are done regularly (including air & fuel filter).
1995 Pontiac Bonneville Stumbling during acceleration
Possible Causes of Engine Hesitating or Stumbling
Dirty fuel injectors (cleaning the injectors often fixes this).
Bad MAP (manifold absolute pressure) sensor
Bad TPS (throttle position) sensor
Bad or dirty MAF (mass airflow) sensor
Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
Bad gasoline (fuel contaminated with water or too much alcohol)
Sometimes, what feels like a hesitation is actually ignition misfire rather than lean misfire. The causes of ignition misfire may include: Dirty or worn spark plugs
Bad plug wires
Weak ignition coil
Wet plug wires