I have replaced the IAC and the intake gasket when I cleaned the throttle body and I still and having a problem with the idle. When I come to a shop the idle will go to about 400 and bounce to 1000 every 5 seconds. driving down the road i can feel the idle bounce around about 500 RPM every five seconds. I cant seem to find a vacuum leak either but It sounds like its sucking air when idle bounces back up. I also had the vapor canister go bad and charcoal was in the purge solenoid. I changed the canister and cleaned out the purge solenoid and the lines. Any help on this one?

 

When it started this surging I though it was cause the a/c started cycling fast like it was low on freon. but I turn off the a/c and it still does it. I now think the a/c may be cycling on and off cause of what is making the idle surge...

 

Throttle positioning sensor. TPS for short. Replace it and your problem will go away.

 

Would the tps be causing it to make a vacuum sound when it idles up?

 

No it wouldn't and i missed that first time around but you may just be hearing the IAC trying to keep up with the faulty TPS. A quick way to check the TPS is to get a Haynes or Chiltons manual and a multi meter and follow the procedure on back probing the TPS and see if the voltage is within spec. To check for vacuum leaks, with the truck running, you can spray some carb cleaner in the area where you hear the vacuum sound and that will confirm or deny whether you have a leak or not. Be careful not to spray around exhaust parts

 

Another potential cause is a weak/dying battery. Extreme heat and cold are the biggest killers of batteries. The IAC doesn't seem to like a drop in voltage.