I have a 1994 f150 with 162k miles. recently the engine would idle for a couple of minutes and then die. Once you get going it's ok. What's going on?
Genesis

 

Are you getting a check engine light display?
I had a '94 F150 with a 302 and it would start up with a very high idle (+3,500 RPM) and then dip very low (-700 RPM) and sometimes the it would smooth and drive and sometimes it would die.
I had the idle air control (IAC) valve cleaned and the problem was solved.

 

There is no CEL visible. Where is the idle air control valve. If it's handy, I'll try cleaning it with something like carb cleaner if that's the right thing to do.

 

It has been many years since I performed this task but I believe on my V8 302 it was bolted on to the throttle-body. There is one electrical connection that needs to be disconnected and two bolts that need to be removed. Then, the IAC comes off very easily and it can be cleaned with carb cleaner.
I'd refer to a manual for a picture of the IAC or maybe try "google" or searching old threads on this site.