Hey guys hope you can help? I got a check engine light on the other day on my 97 e420, got the car scanned and it says that i have a cylinder #8 misfire. Also when stoped the car does have a rough idle and bad exhaust smell? When i leave a light it all runs fine at all other speeds? I checked the basics (spark plug, wires, connections) they all seem ok.....wondering if anyone else experience this and could shed some light?

 

your VIN?

 

pull the vac. line off the fuel regulator on the top of the engine and see if any fuel comes out of the fitting. If it does you need a fuel regulator

 

Same thing just happened with my 97 E420--runs rough at idle, check engine light on, runs fairly well with acceleration. This can be caused by a misfire, when the spark arcs with the engine instead of with the plug. I found at least one spark plug boot that looked chewed up, and another plug looked much darker when I changed them. [:@] Replacement boots are available at Mercedes dealers for around $25 each. I would change the #8 boot (and any others that look bad) and I'll bet that will fix your problem. Good luck!

 

Update for you--I changed a couple of the boots on my E420, still wasn't idling smooth, still with check engine light. Had diagnostics checked at garage, and one of the coils (#2 cylinder) was bad and is being replaced. Each coil costs around $120-150. So I guess it could be plug, boot, or coil that could cause a misfire and check engine warning. Rotten egg smell is from burning an incorrect fuel/air mixture in that cylinder due to firing at the wrong time in the cycle.