02 525i auto, service engine soon, misfire
history first. I had the car detailed and they pressure washed under the hood (without my knowledge). Soon after the "service engine soon" light came on. There were no secondary indicators of trouble at that time. A few days later I noticed the car would start to misfire if it idled for more than 5 minutes or so. I could correct the problem by turning it off and restarting it. Once it started to misfire, if I drove it without turning it off and on again, it would continue to misfire, like it had dropped a cylinder. Under normal driving it seems to drive fine as long as I don't let it idle for a while prior. I've also noticed that there is a "hissing" sound coming from under the hood now. It seems to be coming from the left (driver) side and does not change in pitch with engine rpm changes, it stays constant, and slowly diminishes over about 3 or 4 seconds after I shut the vehicle off.
I'm stumped, any clues would be greatly appreciated.