I have a 2001 X308 VDP that just showed a Check Engine Light & rough running when it was in for yearly Texas state inspection. Following this, it initially showed various P03xx codes when I changed coils & plugs & reset codes multiple times. Now it shows P0301-P0304 and P0354 codes. I would have thought coils 1-4 were bad but I changed them multiple times. Any thoughts- I am at a loss? Should I replace all 1-4 coils now or is there something else I am missing? Thanks.

Maybe timing off on right bank? Have your secondary tensioners been renewed? Also, trace back all ignition wiring on right bank for possible intermittent grounding; look for loose wires from MAF and ECU.

Can you swap the suspect coils to the other bank and see if the 4 codes change to the other 4 cylinders? Then you know for a fact its the coils, not wiring, oil in the plugwells or anything else.

Don't forget please, that code is also associated with vacuum leaks.