Need advice resolving a misfire code (P0300-P0306) on all cylinders on a ‘05 EXL. The current mileage is 96k. Here’s a quick background…
Valves adjusted at 91k miles due to loud tapping sound. The dealer said valves were significantly out of adjustment on the back bank and wanted to tear down the cylinder head to check the VTEC system. Due to my job status, I passed on the additional diagnostic work and just had the valves adjusted. The engine sounds great and the adjustment seemed to solve the problem.
At about 95k miles, the CEL started to come on intermittently. Dealer diagnosed code P0420 and replaced the catalytic converter. (This may be unrelated but threw this in just in case.)
Now, at 96k, the CEL comes on intermittently due to misfire codes. They want to tear down the cylinder head again thinking it may be the VTEC system on the back bank. I am not comfortable this is the best approach since misfire is on both banks. The engine runs well but is slightly rough when cold.
The job situation hasn’t changed so I can’t throw a lot of money at this but don’t want to ruin a new catalytic converter. We bought this new and the van is otherwise in fairly good shape.
Any advice on a course of action to pinpoint the problem or otherwise eliminate less expensive causes?