Gregm

Yesterday I went through the procedures for blasting the intake valves. Everything went as expected and no issues during the process. After everything was buttoned up, the engine started fine and all seemed smooth for the first minute. After the idle serttled down the engine started a stumble and slight knock.
Scanned and got a code of P303 - cylinder 3 misfire. Cleared the code and started again and everything seemed fine until it did it again. Pulled the cover off and pulled the coil and plug (which were both changed 30 days prior with correct OEM and no issues). Plug looked pretty good but one of the electrode gaps was opened slightly. I adjusted gap, quick clean with rag and MAF cleaner and reinstalled.
Cleared codes, restarted and ran fine for about 10 minutes so I decided to take it for a spin. Ran fine for about 2 miles of easy driving. Started giving a little more throttle to about 3k rpm and no issues. Took it up to around 4K rpm with a little more load and then it started misfiring again. Turned it off and this time p0303 and p0306 (cylinder 6). Cleared codes and ran fine to get home.

What would be causing this thing to misfire from just walnut blasting? The procedure only requires removal of intake manifold and some electrical connectors (OP, throttle body, pcv heater, map, etc. everything went back together well.

Any thought would be appreciated

Kaane

Sounds like a bad injector or bad coil. I'd swap coils from another cylinder first. Who did the walnut blasting? P0303 is cylinder 3 misfire, p0306 is cylinder 6, so do you have both codes?

Gregm

The injectors, coils and plugs are all good. It must have been a vacuum leak some where causing a loss of power. Took it all back down and put it back together making sure everything was correct and it has been working perfect