Q: engine light-p303 cylinder 3 misfire, changed spark plugs,ingition coil and cylinder valves

Coils and plugs are usually the starting point for a misfire code, but some basic diagnostic work might save you some money. Sometimes I like to try swapping components from cylinder to cylinder to see if the misfire moves before buying expensive parts. There are a few other problems that could lead to a P0303, like ignition primary problems, vacuum leaks, or bad injectors, but those things are usually accompanied by other codes. It’s clear that you have a dead miss. When the ECU sees a consistent misfire, it shuts off the fuel to that cylinder to prevent damage to the catalyst. The the CEL will start blinking to warn you that you may be doing damage by continuing to drive. You’re at a point where you need to have a professional do some diagnostic work. by contacting Your Mechanic, you can have a technician come to your home or office to check out your misfiring VW and recommend a fix.