Diagnosing OBDII code, could use some help 2003 C4S
 

Car has been running well up to today. Got in the car started it and the CEL came on. The car misfires under load but free revs without issue although I am detecting a slight misfire when at idle. Checked to see what codes were thrown and got four. P0300(multi cyl misfire), P301(cyl 1 misfire), P0303(cyl 3 misfire), P0305(cyl 5 misfire). Sounds like whatever controls cylinders 1, 3, and 5 is not happy. Any thoughts or suggestions? Don't have the Bentley service manual yet, but I guess its in my immediate future.

Well, I might chalk this one up to a wet engine. What I didn't mention in my first post was that I had just picked it up from Esoteric Detailers after having a Suntek clear wrap applied to the front clip. I also had the complete car detailed and clear sealed. I suspect that the coil packs got wet (during the prep) because after I cleared the codes the car runs as it should. Drove it to work this morning (40 miles) without issue. I've been told that the drivers side of the engine in particular is susceptible to misfires if the coil packs get soaked. I'll update this post as necessary if things change. Warren

These sorts of problems are usually due to the coil packs having cracks in their housings. Normally, the car should be able to drive in torrential downpour conditions where the rear tires will drench the engine. Might be worth a look before the rainy season begins.

I failed to mention though that I had run the fuel tank to within 40 miles of being empty. After filling the tank and clearing the code i haven't had an issue. I'm thinking I picked up some garbage in the bottom of the tank causing the misfire. I'm coming up on 75K and so I will be checking the plugs and will inspect the coil packs. Thanks, Warren