My 1990 F150 (302 automatic) has been giving me trouble lately. When I first start it in the morning or after it has set to a while, it will sometimes run rough and blow lost of black smoke. I know that it is running rich but I can't figure out why. It will often die and be very hard to restart. Once I get it started, it will run really rough (i have to hold it at 2k just to keep it running) and then just clear up. Once I finally get it running, it runs great until it does it again. It has 35lbs. of fuel pressure at idle. It only does this about twice a week. WHat could it be?

Sticking IAC solenoid?
Try pulling it and cleaning it

if the iac does not do the trick, may want to change the engine coolant temp sensor.

I used a scan tool to check the codes and it also checks this engine sensors. All of the sensors showed to be good. It is also NOT showing a "check engine" light. It did have a continuous memory code about EGR flow and the air pump not working. Other than that everything checked out good. Is it possible to have a bad IAC or temp. sensor and it not show up on the scanner?

if the iac is just sticking it may not set a code. i have also seen a temp sensor be at the bottom of the talerance, thus not setting a code but still cause problems. i would start by cleaning the iac, then if that did not help then change the temp sensor.