Mercedes :: 1992 - Cranky When Not Used Daily

My car is causing a whining noise. Sadly, the whining is coming from me. The whining started when I talked to the dealer about solving a reliably intermittent problem the car has. It went something like this: The dealer: “We are not sure what is causing the problem, but our tests show that the wiring harness is showing a lot of faults. We recommend that you replace the upper and maybe lower wiring harnesses.”

My car has had this reliably intermittent problem for several years, and I have not been able to find an answer on how to remedy the problem, and thereby eliminate my whining. My car is a ’92 Mercedes 400e. It has about 135 thousand miles on the odometer. I’ve had the car for about 13 years.

Here is the reason for my whining: The car is reliable as long as I drive it daily. If I let it sit for more than a day or 2, the car will start right up, and run and idle great for about 15 minutes. After that it starts to sputter a lot at idle and when pulling away from a stop. Sometimes it stalls while at idle or pulling away from a stop. It does this even if I turn off all the electrical things that I can. If I run the tach up to about 1500 rpm, no sputtering…until I come to a stop.

Once the car starts to behave all sputtery, I usually let it rest for about 30 minutes or so, and after that the car starts right up and usually runs fine. If the car sits for longer than 2 days, it takes more trips before it starts to behave again.

I’ve found the easiest way to avoid this problem is to use the car daily. Of course, I don’t drive every day and every time I let it sit for a couple of days it’s back to being meister misfire.

This has been an intermittent problem for several years. I’ve had a complete tune up by the dealer, which actually worked for a couple of months, but the problem came back. Most recently the dealer replaced the rotor caps (it had been about 35 thousand miles since they were last replaced) and again this worked, but only for a few weeks.

The dealer can’t provide an answer. Their latest guess the wiring harnesses - and that’s where my whining noises started.

The car is garaged when not in use, but I’ve found that keeping inside or out does not affect this problem, nor does it being warm or cool, nor does a lot of rain or a little rain (I live in Seattle, where the only thing that changes about rain is the temperature).

What might be causing the car’s cranky behavior, other than the part where the car is over 20 years old?