Hunting idle, revs up and down

[HVAC SuperTech]

Got a friend of mine who has a 1999 F-350, Auto. It has 208,xxx miles on it. at idle in park or drive, while sitting at a stop light or whatever, it wants to start hunting for idle speed. It revs up and down, maybe 300 rpms or so. when foot is steady on the accelerator in park, it does the same thing, it wont hold a constant idle. Its always fluctuating.

We think its the TPS, but not sure.
he had a mechanic replace some sensor on the side of the engine(he couldnt tell me what sensor) and was told that would correct his problem. it hasnt and hes wanting to know whats up.

Any help is greatly appreciated!

[HVAC SuperTech]

bumping this up. need some help guys.