I recently swapped a D15 b single vtec engine in my 93 ferio. Everythin went smooth apart frm idle revs. I have swapped 3 stepper motors, checked the wiring over and over but no joy. The problem specifically is tht the idle revs drop after the car warms up. Its an automatic car, sometimes the revs are smooth other times they drop to the point where it stalls the car( the car is automatic). I want the idle revs to be smooth and stable by the way the stepper motor works whn the ac is turned on or the fan kicks in. I hope memebers understand the question and help me in this regard.