I've got a 1991 Volvo 240, automatic trans, with 2.4L engine. I've replaced the 02 sensor, Catalytic converter, fuel pressure regulator, spark plugs, plug wires, distributor cap, and Throttle Position Sensor. It still runs rich and within 100 miles every spark plug gets covered in fluffy black gunk and I have to clean them off with a toothbrush. I'll pull the battery cable to reset the codes, and it seems to run fine, but after driving it for about 10 minutes, the Check Engine light comes on and stays on as soon as I come to a stop and it's idling. It doesn't go off after that, even when I restart the car.

It throws codes 213, 113, and 232. The TPS is brand new and I've adjusted it many times to fix the code. I've also cleaned the throttle body and I noticed there was a thin coating of oil in the air tube from the airbox to the throttle body. Is this normal? Could this have wrecked the Air Mass Meter or the Idle Air Control valve and caused the rich condition? Or does this sound like a bad temperature sensor or something else?

All help greatly appreciated!