So im idling high...around 1500-1600 rpms. Once in reverse or drive, revs return to normal range (850-900rpms). Im thinking IAC, anyone else care to agree or correct me?

 

IAC or TPS if the IAC isn't at fault.

Can't you take it off and check to see if it functions correctly?

I think you push the plunger in while the truck is off, then key "on" without turning the motor over. If it moves back to the right position I think its suppose to work right.

This is all off the top of my overworked brain, so I could be confusing this with something else.

 

check the vac line from the map to the side of the throttle body. mine cracked and had the same symptoms.

 

yea, it shouldnt be my TPS cuz i just replaced that a fe weeks ago. thought it may have been the IAC i just dont know how to test it really. Roamer, ill check out that vacuum line...im thinking it SHOULD be ok because the p/o replaced all the CCV/vacuum tubes under the hood.

So the ol' "plunger in while the truck is off, then key "on" without turning the motor over. If it moves back to the right position I think its suppose to work right" should tell me is the IAC is in good working order? im also assuming a good cleaning of it may help as well

 

I sit possible that my IAC has seized up? i mean, when i took it off and tried to depress the little shaft/plunger thingy, it doesnt move. Well, it moves maybe about a millimeter if even that and its not really enough to tell either when its down or up

and i checked that vacuum tube and i beleive that it is new. no cracks or buildup or anything really with it

 

I had this problem. follow your vacumm line down from your map senser on the fire wall. it goes into the side of your throttle body. he little rubber bushing fell out of the side of my throttle body. Same line in the picture above. i pushed it back in . The RPM's instantly dropped. hope this helps