running rich when not pluged in

my 1991 ford f-150 5.8l when not pluged in will flood it self and runs real rich. It feels like it got a bad miss so if i get in and drive it after a 2 miles it cures it self and no longer runs rich. Would it be the temp. sensor. Has 254,000 km on it. also when it warn it idles rough and there should be no reason for the timing to be off.

When what is not plugged in?  Does it smoke out the tailpipe?  Have you done any maintance like tuneup to it?Give us a little more info, please.  Lee
 

sorry i live in SK. Canada and it is winter time here. so when it gets cold i ussauly plug in the block heater. It has new plugs and wires, fuel filter and pump. When i do not plug in the block heater it runs real rich with smoke and black exaught pooring out the tail pipes. sometimes it is so bad it misses and back fires until i drive it to burn that extra gas off the plugs. Then it does not run rich when the block is warm. So when it pluged in the morning the block is warmer and burn that extra gas. It got me baffaled

What's your fuel pressure warm and cold? Could be a TP sensor, ECT sensor, fuel pressure regulator, etc...

the fuel pressure is almost the same hot and cold. i unplugged the egr valve. and it still runs really rich but not fluiding it self like it was when the block is cold. would this tell you something before i go and by all these sensor to try and don't cure it.

What is the actual fuel pressure?  I wouldn't just start throwing parts at it til you get more info, that would cost way too much money, but you could try checking the voltages on them to get a better idea of where to start.