codes 304,305,306 cylinder misfire
 

Hi just got codes,1999 boxster with 74k.Drives well till you hit 3500-4000 revs then splutters badly,brand new plugs have been fitted. codes are 304 cylinder misfire,305 cylinder misfire and 306 cylinder misfire.Could all 3 coils go at once?Has anyone had this problem? does anyone know how to cure this? All advice would be greatly appreciated as this is driving me crazy.

First thing I would do would be to try switching the coil packs from the right cylinder bank to the left cylinder bank, and see if the misfire switches banks, or if it stays put.

Quick, easy, and doesn't cost you a dime.

BC.

What ended up being the cause? I have the same thing, but cylinders 1,2 $3. I'm thinking cam shift sensor since it would affect all 3 cylinders on one side,but would live to know what your cause was.

I got a 306 from the fuel injector wire being loose. Once snapped in properly, no problem.

First check wires, Coils and plugs
Got a couple PO300, 0301, 030#, just pending then went away. Pulled Coils and several had cracking. Replaced all coils and plugs. Plugs didn't seem very tight as well. To soon to know if that was ultimate fix, haven't driven enough miles without CELs to know.