What causes smoke from exhaust when decelerating?

Smoke from the exhaust during deceleration can be caused by several factors, including rich fuel mixtures, oil burning, or a malfunctioning engine component. When decelerating, the engine may temporarily run richer, leading to unburned fuel entering the exhaust system. Additionally, worn piston rings or valve seals can allow oil to seep into the combustion chamber, resulting in blue or gray smoke. This issue often indicates underlying problems that may require inspection and repair.