With a warm engine in my 2000 with 5.4, the rpm's will drop to 4-500 rpm when going from drive to reverse and back to drive, like pulling out of a parking spot. At 219,000, I've not experienced it in the past it seems. Does this have something to do with the tranny engaging and bogging the engine? Or am I crazy and this is normal?

 

Clarification, rpm's drop when gears change and then rebound. Throttle body has been cleaned. I've swapped back from a CAI to the stock airway with a dry flow AEM filter.

 

The IAC is supposed to account for load from the torque converter.
Did you clean or replace it?
The drop to 500 rpm tells me it's not working.
Good luck.

 

I did replace it during the cleaning with a motorcraft one.

 

I agree bluegrass. The idle rpms don't increase due to air conditioning load either. The idle speed is the same with ac on or off. The connection to the iac is good, so maybe a bad one?

 

Your idle should stay about the same with A/C on or off. Its the IAC's function to control and maintain idle rpm with any given load on the engine. The exception being when idling in gear. My 99 F-150 with a 5.4L drops to about 500 to 525 when I put it in drive or reverse, and return to the 700+- when I put it back in park. It (IAC) still tries to stabilize the rpm, but I think it is just set a little lower in the PCM tables when in gear.