Cold start . Rpm dips

[Ivano2937]

Is the engine dirty?
Did you get grease or oil moved around as you changed the IAC?
You sure it not heat burning off oil or grease.
If the engine is dirty, take it to a car wash and wash off the engine, see if the smell goes away.

So it turns out one of the injectors has a rubber that's going loose?
How hard is this to fix myself? It seems like it needs to be readjusted?

[RickHaleParker]

Align and Tap ... Tap! it back down with a rubber mallet. Make sure you don't damage the O-Ring.

[QUARKS40]

Align and Tap ... Tap! it back down with a rubber mallet. Make sure you don't damage the O-Ring.

+1
If you do damage it though, the fix is to remove the fuel rail, which is easily done, but when you do, you will remove all the fuel injectors with it, except possibly the one with the damaged o-ring in your case. You will want to replace all the o-rings at that time, top and bottom, of all the injectors. you'll need p/n 30731083 qty 4
I have some questions though..........
How many miles on this vehicle?
How long do you plan to keep it ?