400E idles rough in gear
 

Just today my 92 400E started to idle a little rough when its in gear. Could it be a spark plug wire or a bad boot that is causing this? How do I go about diagnosing it? Im dreading that it will be a bad wire harness? anyone had this happen to them? Its not bad, but noticable, and it doesnt do it consistently. The car starts fine, whether cold or hot, and accelerates very strongly. I think I may need a new thermostat because it runs consistently a hair under 80 degrees.


Another thing that is a little off the subject, the bass speaker in the pass side door makes a cracking and popping noises when I turn the radio up loud. Where Can I find a replacement speaker?


Thanks for all advice.

-Andy

*** UPDATE ***
 

I just discovered that the wiring harness on my car is bad. I looked at some of the fuel injection wires and they were bare underneath. What should I do? Are they really covered under warranty until 125,000 miles? :confused:

I hope so.

I have a 92 400E as well. If you have noticed your woring insulation is burnt, I would highly recommend replacing the harness. Your issues will only get worse if your harness is damaged as you described.

When I was suspicious of my harness, I called my local MB dealer and spoke with the service manager. He advised me that, depending upon the maintenance record of the vehicle and mileage, MB has been known to perform a "good will" or courtesy repair where MB pays all or part of the cost. It's an individual issue.

In my case, the harness was fine. I replaced by dist caps and rotors..HUGE improvement. I still have a slight rough idle every now and them. My shop did a detailed diagnostic and found that I have fuel injectors that are weak...ie..leak slighly under PSI..plus a fuel PSI regulator that is keeping fuel PSI in the fuel rail a bit too high.. one of those things that one tolerates until it becomes severe..unless you don't mind dropping a thousand or two to replace 8 injectors and a regulator.

Good luck....