W210 P0410 code
 

P0410 Code keeps reappearing on my 1997 E420. I have replaced switch-over valve, oxygen sensor and the check valve for the secondary air pump. I have checked electrical to the air pump and all vacuum connections.

I am out of ideas. What else could throw this code? Am I missing something?

The passages in the cyl heads are plugged with carbon. Never seen a 119 that could be cleaned out without pulling the heads off.

What would this carbon be caused by? and how much cost can I expect from an indie? Is it worth it if I have it fixed?

Car has 240K on it, runs like a champ, well taken car of...at least since I have owned it.

The passages are small and are exposed to the exhaust stream but dont have enough heat and flow to keep carbon from slowly building up. Will probably cost near what the car is worth. Best advice = just live with it.

I agree. I don't know what the emission laws are in your area, but here in Wa paying for a wavier for the next 10 years would be a fraction of what it would cost to repair.