[Zoom This]

I have had the same idle issue on my 418W in SPF 1735. Old motor did it, new motor does it. New carb, new MSD Pro billet distributor. Still idles high then slowly drops at a stop. Believe me, I've done everything possible to the distributor and carb. My theory? Motor and idle mixture is just fine when the car is moving and cool air is being ingested. When the car comes to a stop, the motor is now inhaling hot air. This equates to a richened fuel mix at idle, thus bringing the mixture to a rich condition and a lowered idle. It's the same thing as turning the idle mix screws in a half turn or so when the hood is down and the car is at a stop. Try driving down a long hill when the motor is at full operating temp. Put the car in neutral and watch the idle. It stays at 1200 rpm. At least mine does. Bring the car to a stop and within 10-15 seconds the motor is now idling where it was intended to, 900-950 rpm. I'm done chasing a percieved mechanical problem. It's the heat under the hood.