Recently, I have had some rough idling problems with my 1986 mustang gt with gt40 heads and intake off of an explorer. I have changed many things on the car to try to fix the problem of it idling up and down between 500-1100 on a cold start, and also when barley throttling down on the motor it wants to stall and even sometimes die. Its like it stalls and loses 200 rpms and then will catch itself back up. I have changed the TPS, IAC, and have changed plugs, wires, cap, and rotor button but none of these seemed to help the stall. What should I do?