In the past three days, my otherwise perfect C240 (2.4) has developed a bit of an intermittent misfire complete with lumpy idle. The fault just occured, no hints or signs. I first noticed it when there was a momentary loss in power when pressing the loud pedal followed by one or two small bursts of lumpy idling when sat at junctions. Once revs were past 1500rpm things were fine. Today things started off fine when I went to work, small amount of lumpy idle at traffic lights, but other than that off to work fine. On the way back today the car started fine, I drove a mile then suffered a fair bit of loss in power along with a misfire all the way. Seeing as i had no option but to get home (50 mile journey) i persisted and mad it home albeit on what sounded like 5 cylinders. When I got home, the misfire was still there as i reversed into my parking space. I turned off for about 40 seconds, went in the house to do stuff, came out, started her back up and everything was fine, all back to normal. I've done 3 separate 1 mile journeys in the last couple of hours to check her out and has been fine again. Any suggestions as to what this could be? My gut reaction is the wet weather we have been having and i've done a fair bit of mileage (Swansea > Brighton, 50 miles in between then Brighton > Swansea) in the past 5 days and i've gone though a good amount of large unavoidable puddles in the roads, etc. Coil packs have been checked, connections reseated, MAF has been checked, etc. Does anyone know the location of the ECU, is it the black box where the diagnostic plug is situated under the bonnet? Thanks for all your help.