I've got a 1998 Accord EX V6 with 170K miles. I'm the original owner and have had all service done per the manual by a reputable local shop (not the dealer). The car runs great. 6 Months ago the check engine light came on. The local shop looked at it and could read the engine codes but couldn't find any problem that caused the check engine light to come on. I'm getting misfire codes on all 6 cylinders and also get a catt efficiency code. Again, the car runs fine.

I took the car to the local Honda Dealer and they first thought it may be the catalytic converter but after looking into it they don't think that's the problem. The spark plugs are fine. They're telling me they want to change the EGR valve for $275 but can't promise that will be the fix. If that doesn't work they'll keep digging. My problem is that I don't have the greatest level of confidence in their shop but my mechanic can't determine what the cause is either.

Any ideas?