My Mazda 3 2.2 diesel shakes when starting up even when using auto stop/start in traffic or at a red light. I took it to a mechanic and they checked the clutch kit and flywheel but did not resolve it. Car shakes especially when the engine is warm. The mechanic changed the drive belt too. Thank you
Ask your mechanic to check the engine mounts and replace them if they are worn. Loose or worn engine mounts will cause a diesel engine to shake vigorously when it starts or stops.
Diesel engines have a much higher compression ratio than gasoline engines, so the first or last compression stroke that occurs when an engine starts or stops can be a bit violent. Some diesels have an "anti-shudder valve" that momentarily closes the air intake when the engine is shut down to rarify the air in the intake manifold and make shutdown more gentle. This doesn't work, of course on start-up.