GoingHaam

Hello everyone I have been on this site for a while just not posting, but i have a 2002 Mustang GT Convertible Auto, not too long ago my oil pump went out and and i locked up my motor, well now i have a new (used) motor and it has a slight miss in it when it is coasting at a constant speed with my foot on the gas, it doesnt miss during idle, acceleration, or deceleration, just coasting it only does it for the first 15 to 20 mins of driving, until i cut the car off the the time cycle restarts .. it was complete motor, with about 80k just took what they gave me and dropped it in...

any clue of what this problem may be?