Started the car this morning, and left it idle for 3 odd mins..
CEL light on, misfire on 3 cylinders noted.
CEL light went away a min or so after.
I cleared the code and the car drove fine to work.
So seems to be a cold start issue.. will know more over the next few days.
Found this..
https://www.renntech.org/forums/topic/37022-997-gen-1-2006-c4s-misfire/
And got this from it:
I think I have the answer, or at least I hope I do. My 2005 C2 is in the shop for cold start misfires. Runs great, the only thing obviously wrong was the check engine light. However, the fault codes indicate random cold start misfires in all cylinders. I've had my software updated twice, plugs changed and compression checked. Interventions have led to the light going off for brief periods of time, from a week to as long as several months, but it hasn't lasted.
Turns out, a certain number of the 1st 2 yrs of the 997 (2005, 2006) have had problems with the lifters. A slow leak allows the oil to drain out over time, which causes the lifter to function suboptimally. If the car is cold, there will be misfires on startup until the fluid pressure builds back up in the lifter.
This is a documented problem that Porsche technicians should be able to look up. The fix appears to be replacing the lifters. I'm waiting to sort things out with my warranty people and am hoping this will fix my problem. Sounds reasonable enough to me. See if your mechanics think this is a possible cause for your problems.
Also I have a BmC filter – my stock filters gone missing..thinking should I buy ther original one to see if this works?