I ran out of gas in my 91 w150 318 so I poured in five gals I had in my toolbox filled up and drove 100 miles as soon as I stopped the truck shut off. it won't start unless I'm on the throttle and drives just fine until you come to a stop. If it was old or even watery gas wouldn't it affect the driving not just the idle? I'm thinkin it's the idle control unit maybe a short somewhere or a loose plug. Any ideas?

 

Check the plug on the AIS motor on the drivers side of the throttle body.