i have a 97 f-150truck that when ever i start it it will not stay started unless i have my foot on the gas as soon as i let of the gas it dies

 

Check into the IAC

 

I had the same problem.#1 change the EEC relay and the fuel pump relay. they are cheap and and just might fix it.
#2 clean and check the idle air control valve
#3 do not change the set screw on the throttle plate , it is pre set from ford.
good luck.

 

yeppers try cleaning the throttle plates an cleaning the IAC like cctxfish suggested , thats usually the problem , there gummed up , just use some carb cleaner an a old tooth brush on the throttle plates an dont forget to clean the back side as well as the inner bore where the plates ride , on the IAC, just spray it let it sit a few minutes an spray it again , then go for test drive , your idle should be like close 900 rpm , it may be a lil hard to start at first till it swallows the carb cleaner so dont get worried

 

my buddy had a 92 f-250 with the same problem it was a vacuum leak (the hose fell off)