2
questions

From time to time right after starting, the engine begins mis-firing and the check engine light comes on. I took to local Mercedes dealership and their equipment showed a mis fire on 1, 4, and 5. We replaced the plugs and a few days later the problem has returned. If I turn the vehicle off and immediately back on, the mis-fire goes away (Check engine stays on).

This vehicle is in excellent repair overall and I have done all the typical maintenances etc.

What could possibly cause this after replacing the plugs???????

What is the recommended interval for the timing belt