99 gt idle quality

I have a 99 GT with a few minor bolt ons. Flows, Xpipe, 3:55 and short shifter. I put the MIL eliminators on the car and they worked fine for about a month. The check engine light came on. Now the idle is fine when the car is first started but when I stop somewhere and get back in to go the idle will surge from 200 to 1100 RPMs until finally falling into place at 750. I have replaced and cleaned the IAC valve to no avail. Also after the light appeared I have noticed a hesitation in the lower RPMs. Can these be related? Does anyone have a possible solution? If so please respond, thanks.

Yes they are related. The 99-up newer stangs are a lot pickier when not using cats or even hi-flow cats. Also the MIL Eliminators have been know not to work all the time on the 99-up Stangs. You need to get a custom burned chip(Diablo, Autologic etc..,) to keep the check engine light off and fix the issues you are having.

The Mils I got work fine. Just the ghetto rigged 02 censor we have on the Xpipe went out. Get another set from Dallas Mustangs?

I have used Dallas Mustang one's plenty of times and they work off and on