190E 16v with lumpy idle for the past 6 years - PeachParts Mercedes-Benz Forum

pentoman · #1 12-17-2011, 08:59 AM

Hi all, my 190E 16v runs with a lumpy idle at around 1000rpm. It has always done this and I've owned it for 6 years. It doesn't exhibit any other major problems - e.g. it produces good power, it doesn't stall, it starts as well as a 20 year old car should. The only thing abnormal is that it seems to need a new distributor cap every couple of years.

During the 6 years I have owned it, it has always had this lumpy idle. It's an irregular misfire. It's quite subtle, and you mostly just feel it as a shaking of the car. It goes away when you increase the revs to 1300+. I have compared with another 16v which didn't exhibit the same misfire, it ran more smoothly.

During my ownership, some of the ignition parts have been replaced. E.g. It has had new plugs (the recommended ones), and it has been through about 3 or 4 distributor rotos and caps. I even have a spare ignition ECU which I tried, it makes no difference. The plug leads and the coil have not been changed because they are more expensive. I did once have the spark tested by a mechanic - it had a really strong spark.

On the fuel system, in my ownership the fuel filter was replaced, the injectors were replaced with brand new ones, And I have tried replacing the whole fuel metering setup with a spare that I purchased from another car of the same year. None of this made a noticeable difference.

On the air system, I just replaced the main air pipes for the PCV, the IACV, and the ones to the injectors, with brand new pipes (actually I have one more still left to do). My gauge reads 15in of vacuum, at idle.

The top-end of the engine has even been rebuilt with new valves etc and, still the stumble at idle remains exactly as it did before. An irregular stumble that you feel through the seat of your pants.

So, what have I missed and what else can I check? What can I investigate to give me some clues as to the cause of the problem? Could this be purely a characteristic which I will have to live with? It's not major, but I am curious to see what causes it and how it has persevered for so long.