Originally Posted by edub370

a)does your car have cats?

b) even if it doesnt, cars runs rich at idle. its called open loop. basically what your car does is ignore the signal from the o2 sensor when first turned on. it strictly works from signals based on your maf, and whatever has been pre programmed into the cars ecu to ensure it gets to proper operating temp quicky. that means warming up the cat, coolant, or any other parameters that the ecu is looking for. once those are met then the car goes into closed loop. which means the car then starts talking to the o2 sensor to see what kind of adjustments need to be made to optomize your afr and engines performance.

thats why all vehicles idle higher/rougher and smell like gas more when they first start. that gets exagerated when you remove the cats because any excess fuel that is left unburnt after combustion can no longer be ignited before exiting the tailpipe