Rough Start (Misfire Code)
 

Lately my Boxster (99' 2,5) have been acting up occasionally during start from cold. It is only now and then. Not every time.

When starting from cold it starts rough. Like its running on 5 cyl. After a little while it throws the CEL. Misfire Cyl3 (P0303 Cylinder 3 misfire) or last time it happened Misfire Cyl2. (P0302 Cylinder 2 misfire). After the rough start, which lasts like 3 - 5 secs, it runs like champ.

Spark plugs are new. AOS new.

What are the likely faults? Coil packs?

How many miles on the odometer? Were there any cracks in the coil packs?

140000KM. Did not see any obvious cracks. But did not study them for cracks either.

"Lately"? How long have you owned the car?

Personally I would replace ALL coil packs. Easy job. I was having same issue not sure of the CEL codes I was getting but I bought 2 coil packs that were throwing CEL. They LOOKED fine. I then decided to replace the rest. Left bank cylinders were throwing the CEL right bank was not. When I replaced the right bank coil packs I couldn't believe the cracks in them! While you are in there you may want to replace spark plugs and tubes and seals. Also if you choose to replace tubes I would go with OEM they are more robust than aftermarket ones.

Lately like in the last couple of weeks. Had the car for a long time.

Sure, easy to do. Coils are about 200 for the Beru set. Just dont like Shot-Gun diagnostics. :-)

Spark plugs are new, so are the tubes and o rings. Did them as part of major service.