This one should be "sticky FAQed"..... to be part of the SC repair manual....PMI said:If the plugs are fouled or have some other problem, you should get the code for a random misfire or similar before engine running rich.
FPR vacuum hose: The fuel pressure regulator uses the intake vacuum to keep the fuel pressure constant relative to the intake air pressure (2.5 bar on most turbos). If the FPR vacuum hose has a leak, the FPR will not regulate correctly, and the amount of fuel from the injectors will be off. The result can be a lean or a rich mixture, depending on intake vacuum/boost.
Front O2 sensor: The ecu detects whether the engine is running lean or rich by using the output of the front O2 sensor. The sensor measures the amount of oxygen left in the exhaust gasses after combustion. The fuel left cannot be measured directly, just the O2. Too much oxygen means the engine is running too lean, too little means it is running rich. If the O2 sensor is old or fouled and cannot detect the amount of oxygen, the ecu may THINK the engine is running too rich or too lean.
MAP sensor: The air pressure sensor is also used by the ecu to regulate the air/fuel mix, but it does not seem to fail very often. There could be a problem with the connector or the hose leading to the sensor though.
TPS: The throttle position sensor tells the ecu how far the throttle is open. Not very likely to fail, because it is a very simple device (basically a single turn potentiometer), but the connector might be loose or need cleaning, etc.
Based on all the bad vacuum hoses I have replaced on my car, I would suspect those first.
Egh, those thousand changes were things like courtesy wipe of the rear windshield when you put the car in reverse....:cheesy:Squoosh!There are those 1000 changes or so between the 900 and 9-3 and I would really like a repair manual that recognizes that. I cant find one anywhere online yet.