Ford Repair: Wont idle - low RPM, mass air sensor, throttle position sensor

Question
Hi Steve!
I have a 1990 F-150 with a 5.0 liter engine.  Lately it does not want to idle... at all... especially when it is cold.  When I first start it it idles at expected RPM for about 20 seconds, then drops to nothing. When I pull up to a stop sign, it will stall.  It is almost like the idle is set too low... but I don't know how to change it on a fuel injected engine.  I set the stop on the throttle itself as far out as possible to keep the throttle from returning as far as it can go trying to increase the idle speed.  It seems worse if I am at full speed and come to a stop quickly, the RPM's drop and it stalls. If I ease to a stop, sometimes it will idle after it is warm.  Any help would be greatly appreciated!

Answer
Doug-

  I'd put money on the throttle body or mass air sensor (although I can't remember if the '90 F-150s have mass air).  Give the throttle body a good cleaning and see if that helps.  I had a very similar problem with my truck (although it's a GMC and I hate it) and cleaning the throttle plate made it at least stop dying.  If that doesn't work you may want to try pulling codes.  Chances are there won't be one, but it's worth a shot.  You might want to check the TPS (throttle position sensor) sensor as well, but the symptoms you described aren't typical of a TPS problem (just trying to cover all of my bases here).  Lastly, if the car is NOT mass air equipped, replace the MAP (manifold absolute pressure) sensor.  Again, I had similar problems in my Mustang before I switched to an aftermarket injection system and replacing the MAP sensor cleared it right up.  I would bet good money that the problem lies in one of those places.  Hope this helps.

Steve