It's been a week since the ATF treatment. Car idles great, but now when I start it up cold it no longer shoots up to 3000rpm—rather, revs up to about 1500–2000 rpm, flutters for a moment then drops to idle. Before the ATF treatment, the car would rev to 3000 rpm, hold there, drop to idle for a moment, then stall. Strange. I'm going to assume that since it does not stall at startup now that the engine is MUCH cleaner (carbon-free) and spins much smoother. Should I be concerned about the 3000rpm startup? The car has the STOCK pre-cat, a newer main cat, and a newer exhaust. I've also modded the TB—removing the cold start system. Any suggestions would be helpful.

rxse7en

 

You should be killing that high idle when it happens by bliping the throttle to bring it down. That is the AWS (accelerated Warm-up System or better known as Accelerated Wear-out System) That is revving the engine for emissions purposes, when the engine doesn't have any oil in the top of it yet.

The drop in your idle could be caused by you stock precat. Do you know if it is clogged or even in one piece still?