Low (or no) idle, 420 - Mercedes-Benz Forum

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post #1 of 2 (permalink) Old 08-25-2004, 05:32 PM Thread Starter
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Date registered: Nov 2002
Vehicle: 300TD, 420 SEL, 560
Location: Marietta, GA
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Low (or no) idle, 420

All the posts I have read are addressing high idle. My problem is the opposite. The engine starts cold and idles fine. In fact, it rarely gives any problem. About once or twice a month, when the engine is hot, it will suddenly refuse to idle. My wife had to have it towed to our mechanic once. He kept it for a week, but it never messed up any and I brought it home. The only time this happens is when the car has been driven for a while, then parked while shopping (15-60 min). It will usually start up OK and then die at the first red light. After we have driven for a few miles, it will usually correct itself and idle OK again. This definately seems to be heat-related. Like I said, this only happens once or twice a month and is driving me crazy.

It did it again today, but was idling OK by the time I got it home. I checked the voltage on the pins to the idle valve. I measured about 3V dc and 13V ac, with the car idling at 600 rpm. I disconnected the plug and the idle increased to over 1000. I don't know whether to measure ac or dc volts and whether to measure across the pins or from pin to ground. Any help would be greatly appreciated. These parts are too expensive to just begin blindly replacing them.
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post #2 of 2 (permalink) Old 08-25-2004, 07:30 PM
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Date registered: Jun 2003
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RE: Low (or no) idle, 420

This is not exactly your problem but close. Please note JEFFMG1’s post about checking EHA current:


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