Lumpy idle and smell of fuel

[Christian H]

Hi Gents,
My Boxster is a 1999 2.5 has covered 67,000 miles and has been pretty much trouble free during the last 10 plus years of ownership.
I have only covered 1,200 miles since the last major service last year but recently I have experienced a lumpy idle and a rich fuel smell that has now illuminated the orange check light on the dash, once on the move the car seems to run reasonable well although maybe a little down on power.
I cleaned the throttle body and checked the intake for leaks and checked the maf sensor (maf was changed a couple of years ago) last week but this made no difference at all.
A friend scanned for codes today and it came back with these generic codes:


P0300 Random/multiple cylinder misfire detected

P0301 Cylinder 1 - Misfire detected

P0302 Cylinder 2 - Misfire detected

P0303 Cylinder 3 - Misfire detected


If it had been one or two misfires I would probably have been looking at coil packs but with them all being on the same side I'm wondering if it could be the o2 sensor on that side of the engine?
Has anyone had a similar experience?
Any advice would be appreciated before I take it to my independent Porsche specialist.

Thanks guys