Engine Performance problem
1990 Volkswagen Rabbit 4 cyl Front Wheel Drive Automatic 213000 miles
Engine runs fine till it gets up to full operating temp. Then it starts to bog down and black smoke starts to come out of exhaust. I can unplug the fuel pressure valve along with the temprature sensor (the blue sensor) and the car runs fine. I plug either one back in and it will die. I have replaced fuel pump, fuel filter, blue temp. Sensor, checked for vacuum leaks. Any ideas would be appreciated.