* Misfire(s): This is the most likely cause. A misfire occurs when one or more cylinders aren't combusting properly. This causes a rough running engine (violent shaking), reduced power, and can lead to unburnt fuel exiting the exhaust as thin, bluish-white smoke. The misfire could be due to:
* Spark plug issues: Worn, fouled, or damaged spark plugs are common culprits.
* Ignition coil problems: A failing ignition coil can prevent a spark reaching the spark plug in one or more cylinders.
* Worn or damaged wires: Cracked or corroded ignition wires can interrupt the spark.
* Faulty PCM (Powertrain Control Module): The PCM controls ignition timing and fuel delivery. A problem here can lead to misfires.
* Low compression: A leak in a piston ring or valve can cause significantly reduced compression in a cylinder, leading to a misfire.
* Vacuum leak: A significant vacuum leak can cause an unstable idle and rough running (shaking), though usually less violent. It might contribute to incomplete combustion and therefore some smoke, but usually not significant.
* Faulty fuel injectors: A clogged or malfunctioning fuel injector can lead to an inconsistent fuel/air mixture, causing misfires and shaking. It could also contribute to smoke.
* Engine mounts: While less likely to cause the puffing smoke, severely worn engine mounts could contribute to the violent shaking. They are designed to isolate the engine from the chassis.
* Camshaft or crankshaft position sensor issues: These sensors are crucial for proper engine timing. A faulty sensor can cause misfires and erratic running.
The thin smoke: The color of the smoke is crucial. Thin, bluish-white smoke usually points to unburnt fuel, supporting the misfire theory. Black smoke would suggest a rich fuel mixture, while blue smoke often means burning oil.
What to do:
You absolutely need a professional mechanic to diagnose this. Trying to troubleshoot this complex issue yourself could damage the engine further. The mechanic will likely use diagnostic tools to identify the specific problem. They'll check for codes, inspect the spark plugs, ignition system, and perform a compression test to pinpoint the root cause.
