ok this is my first time

I just bought a '89 ford f-150 when you start it you have to give it a little gas sometimes and when warming up it will idle fine but when warmed up it will surge from 500 to 1000 rpm.

 

i had the same problem it was the idol control sencer

 

called the IAC bud idle air control sensor

 

The IAC can get carboned up. Sometimes a cleaning will solve the problem.
Sounds like it could also be the TPS “throttle position sensor”.

 

Usually a Vacuum leak. & the IAC is not, nor has it ever been a sensor. It is a solenoid controlled valve. http://www.fordfuelinjection.com/?p=39

 

Fuel pressure regulator or vacuum leak

 

I had the same symptom on my Honda Accord. It was a dirty IAC valve. I cleaned it and a year later all is well. Easy job.

 

i had the same problem then cleaned it with seafoam and it fixed it so id try cleaning it first , good luck

 

i had this problem when i first got my truck started after a long time. it's seemed to stop though now that it's been run a bit more. where is the IAC located? i had to replace a TCP on a nissan a long time ago and i thought that's what it could be. but after my truck warmed up a little it would idle back down, just surge so i don't think that's what it is. my dad's car does the same thing and it's the same motor.

 

which motor do you have?

if you have the six cylinder, follow the black plastic air intake tubes to the metal thing that they go into. that metal thing is the throttle body. its on top of that, sort of a cylindrical metal thing with a black plastic connector on the end.