upsidedown_04

Ive replaced the engine harness.. but it still runs poorly. If in idle with no load it runs perfect. If I rev the motor in neutral it reves roughly but once at high rpm smooths out. If I put it in gear with the brake on it runs rough. Acceleration is rough but at speed seems ok. What now???

EKL

I would check the following things that may affect the idle:

1. Mass airflow sensor
2. Throttle actuator
3. Egr valve function / check to see if the hot inlet pipe to the intake manifold is plugged with carbon from egr vapors.
4. Plugs / wires

upsidedown_04

I FIXED IT!! It was the last coil over cyl 6. F%^*ing eh its fixed!! from the looks of the harness I was sure that it had to be the problem. Capt Jasper said that it could knock out the coils.. you were correct sir!!.. by the way.. I totally re-wired the harness myself. not for the faint of heart to be sure, but it cost me about $75 in materials and one day of nothing but wiring. Thank you for all who responded to my posts! And find attached my message to Mercedes over their superior engineering of this wire harness.

Kestas

I can see you are respectfully pointing at the old harness.

I'm curious, where did you get the stock for rewiring, and are the wires still color-coded?

upsidedown_04

I picked up a variety of wire from Frys electronics and also from Radio Shack. I did not replace the wire from the connection to the ecu but closer to where the wire enters the engine bay proper. The wire was degrading close to the engine presumably from the heat. It seams most experts I talked with recommend splicing over soldier so I went that route. I used heat shrink tube to seal each splice and staggerd my splices. I used different color of wires but the original color codes are not retained all the way through-out. I was more focused on the wire size. I traced out and replaced each wire one at a time to avoid confusion during the process. The car seems to run well so far. If it ever becomes an issue again, Mercedes may well have the last laugh as I will most likely replace with a factory harness. But so far it appears that I may get alot of milage from this. One thing is apparent that its of no worse design than the original!

ashman

If one has the time, why not rewire it yourself.. no harm in it, worst case is you would have had to buy a new harness..

Good job.

You should have documented your progress as a diy article.

Kestas

I already replaced my engine wiring harness with a dealer-bought harness. I still have the old one. If I had thought about it, I probably would have tried to rewire it myself. I know how hard I work for $800, this job would have been worth it.

Plus, I know the rest of the car's wiring is made with the same insulation. I've already experienced problems with stiff insulation elsewhere.