Hello all! On my car, the idle runs fine, then sometimes drops to about 500 rpm. It sometimes feels like its going to stall but it does not. How can i fix this, i dont know where to start...

 

Hi Max,

I have the same car as you. Mine now has 350,000 miles, so I've seen many of the problems. I'm just an owner, not an expert repair person.

In my opinion, the fuel system is the weak point of the whole car. It has been the main focusof most repairs. Over-all the fuel lines and fittings are not stainless so they rust; the rust eventually cloggs the fuel distributor and fuel injectors, changing their performance. The computers can get old and glitchy affecting the mapping and fueling. And most of the other components will just corrode beyond restoration and jam. Its possible, as in my case, that there exists several components that are operating well out of tolerance, rather than just one "bad" part. But at least its not as complicated as the newer cars!

"Someone"or "you" need to test each component to make sure they are working within their tolerances. They will either be "in", "out", or "on the edge", which might as well be out. This requires a drawer-full of special tools, some you can make yourself if you are able. Expect that your mechanic will want to replace a few parts. Seriously, every part must check "in" tolerance. But rest assured, when all parts are "in" tolerance the car will run great!

There are some people in here that CAN identify the exact part with only a few clues. But if you are like me and end up trouble shooting,you will need a diagram of the fuel system and components, a test procedure for each component, specs for each component, and the tools. For example you may hear the fuel pump come "on", but you need to know that it is producing the proper pressure, and also volume. Hearing it come "on" just isn't good enough. There are some sensors and switches that you can check with an ohm meter etc. And just because you find "one " faulty part doesn't mean you are finished; keep checking until you know everything works.

I like the "E-class Owner'sBible". It lacks alot of things, but it does havea cutaway view and explanation of each major component. This will get you pretty far. If the problem is in the computer you will have to take it to a dealer; there is only so much with FI thatcan be done at home.

Blue

 

I have a 1987 190e 2.3 that just developed the same problem...except that about half the time when I come to a stop or turn on the heater or A/C fan the engine shudders and dies. Sometimes it will maintain a 800 rpm idle...sometimes not.

Hope someone can point us in the right direction.

 

Usually, when the performance of my 190 changes, I can narrow it down to about five parts. To find the exact part, I have to test each suspect part. I have found ways over the past 18 years to testmost parts. I still return to the dealer when I need help.

When you have an idle issue, the problem could be several things.I would probably ask myself these questions. 1) is it firing on all six; are you sure? 2)Are all vacuum hoses connected and in good order? 3) Is the air/idle valve working? You can take it off and test it with a regular 9volt battery and a couple of alligator clips. Look in the port; you should see it open and close promptly. 4) Check the rubber cover under air meter; theseare notorius for getting old, dry, cracked, and leaky. 5) For referrence, check the soot in thetail pipe. Is it light grey or black? That's a pretty good start, I think.

Blue