My rpm started jumping up and down recently, espically when the car starts at cold. Is this due to my iacv or is his because of my cel from my test pipe. The rpm/idle do jump every here and there at stop lights. Inputs would help, thanks!

 

The car should run fine with the P0420 code, and I wouldn't jump to it being the iacv either. Mine did that and it was the map scaling and idle stepper table that needed adjusting after installing an after market intake. You can actually take the iacv out (3 little screws) and turn the key to "on" and watch if it is working or not.