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I have a high idle cold or hot m103 motor dealer said i needed a new wiring harness, some times i can turn the engine off and restart and idle is normal but lately not any comments or things to look for!!
1989 300E
 

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1994 E320
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I've had the exact same thing happen to me, and it turned out to be something as simple as the throttle cable needing adjustment and a smear of oil on the linkage. Try that first before you fork out some big money unnecessarily to the dealer.

Hope this helps,
Shady
 

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300TE 4-Matic 300GD
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Hi Joet-1.

Very interesting.

The first question that pops into my mind is, just a new wiring harness, and nothing else? Hm..

To be able to reach such a conclusion, one must first check all involved components, and they must all check out fine. We are talking supply pressure, ECU, rotary idle actuator, throttle switch, and sensor signals. (Yep, actual signals, and not just measuring the sensor) This takes a certain amount of time. Then you must identify a reasonable number of bad wires. If I were to come to you and say you need a new harness, I would be deep into the job already. And it would be fantastic to find each and every component A+ except for the wiring. I have never heard of anything like it.

I always divide a diagnostic mission into two jobs. Part one is finding the fault/s. I never quote a price on that. Proper communication is vital in this fase. I never accept pay if I can't pinpoint a measureable error. Part two is actually fixing it. And in part one, I'm always aware that part two might be done elsewhere.

If it is an offer from an MB dealer, I would take it right away. Then hold him to his word. A new wiring harness isn't cheap even in Germany, and he might have to take some pretty heavy corrective action to get it right. That is going to be your gain.

If it's from a local car shop, they're probably going to call you and say that "hey we found a defective ECU. Whatta you know." Or someting like that.

The M103 is actually very easy to work with, and people with good engineering capabilities usually do very well with pretty basic equipment. One must just obey the laws set up by DIN, (Deutsche Industrie Norm) and the specification OberKommando Stuttgart. One must read documentation. People who know industrial automation systems, are natural candidates to help out real well. They grasp the basic physics, and closed loop systems already, and a W124 is no match for a pro. Many VW mechanics are briliant with CIS-E. Just a tip.

You don't say if you have a lambda sensor or not. But from your description, I suspect you have one. A thermo signal will tell the rotary idle actuator to raise the RPM a little when cold. This signal has a time and and a thermo parameter. If this comes at any given time, it will raise the idle a little. If it comes and goes, the idle will rise and sink accordingly. It doesn't do any damage except high idle, but can effect automatic gear change timing and so on. This could absolutely come from bad wiring. And when it comes and goes just by restarting, it's an indication of bad wires, yes. But even more so, an indication of bad ECU. Or signal jumping in the ECU connector. And actually it could also be bad ground. (earth)

I would monitor pin 21 and 8 on the ECU (N3). If fine values, check trafic over pin 13. Check wire between pin 1 on EZL wheel (N1/2) and temperature sensor B11/2 (green-black). The green-red goes to pin 21 on the ECU.

Remember, bugs breed. One now could be several tomorrow.


Regards.

Geir
 
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