My "check engine" light won't go away. After three or four "costly" services, the light comes on for a few days and then goes off for a week or so, and then comes back on again. This began in October last year. One Honda agency's diagnosis was "cleared DTCS and tested system and observed normal engine operation. Fuel trims are within spec and misfire monitors detected no misfire. One possible cause for all cylinder misfire is EGR valve malfunction. EGR tested normal. No correction performed." Yet problem persisted. I took car to a Honda mechanic who replaced EGR valve. Yet problem persisted. Took car back and same mechanic replaced the spark plugs. Idiot light came back on today. After almost $500 and no solution to the problem, I am obviously frustrated. What's my next step?