My 94 E320 developed a "hunting idle" problem which has been almost completely repaired, but I could use some expert advice.
When the hunting idle occured, the cel and radiator light had already been on for a while.I was assured the radiator light was a sensor and the original diagnosis for the cel was an oxygen sensor, which was replaced in a local shop. When it didn't repair the hunting idle issue, I took it to a mercedes specialist. (Please forgive me for not doing my own work. I'm a Mom with limited mechanical ability) The specialist was unable to diagnose it withhis computer and using his expertise, replaced the throttle actuator and mass air meter, replaced the neutral safety switch (which was faulty), and shut off the low coolant light. In addition, a few breather hoses were replaced. The hunting idle was somewhat better, but it would idle at 30 mph and rev up spontaneously. About a week later, the water pump went and was replaced as was the serpentine belt. The overload relay was replaced but was not malfunctioning, so the old one was put back in. (I hope I haven't lost you, I'm taking the info from the receipts)
The car is still idling a bit fast and barely noticeably hunting. A few times when I've put it into park, the idle revs up to an uncomfortable sounding place. I don't recall the number, but the needle was straight up on the tach. After I hit the accelarator pedal a few times, it came back down. The last frustration is that after having all this work done, at a far greater expense than I expected or could afford, I was told that the car won't even pass state inspection for emissions because of the idle.
I'm at my wits end and my pockets are almost empty. I won't fault a mechanic using years of expertise to diagnose a problem.I know about using the right tool for the job. I also know that if the right tool isn't working or available, sometimes you make do and as an employee, do as you're told to do. I'm a bit upset that it wasn't made clear that the computer was unable to diagnose the problem. I certainly don't want to give up the car but I have no idea what to do.
If I've been unclear, please let me know.
Thanks in advance for your much needed advice.
Betty

 

sound like a lot is going on here i will need addition info. 1st . sound like the local shop does not have the correct equipt. and or infor to repair the car.not saying what they tried was wrong because these car do go through those parts (mass air , throttle actuator ) . but if he didnot have right scan tool (mercedes benz HHT, or star sds then it may be a problem ) the throttle actuator has to be learned for the engine computer (ME) i have seen sometimes when actuator was pulsing the butterfly flap which could cause surging idle , also vacc leak will send out a lean signal (false info to ME) and it trys to compensate by going rich there could be a # of possibilites. best advise is take to autho. MB dealer pay the diag. fee and advise service advisor of what was replaced give the tech . copies of the past work done normally is a 1hr check out time and they'll tell you the fault codes and whats going on there. who better to trust to repair then the dealership and they'll tell you all that is wrong . good luck

 

Thanks very much for your reply. I had taken it to a certified mercedes specialist, but apparently their star equipment wouldn't work on my car. Your suggestion is exactly what I thought I should do. Now, I just have to make a bit more at work so I can go to a mercedes dealer and have them diagnose it and hopefully find that it's only a minor adjustment on the throttle actuator via the computer.
It's the nicest, most dependable car I've ever driven. Though, as I was warned, quite expensive to repair.
Thanks again, I'll let you know how it goes.