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Old 12-20-2002, 03:17 AM
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Angry 84' 380SL Stalling

Please Help!

I have a 380SL. It currently stalls after driving it for awhile. When I get to a stop light, I see the Tachometer go up and down. It is revving itself on it's own. I usually put the car in Neutral and try and rev the car. Sometimes that helps, most of the time it just stalls on it's own.

I brought the car to my brother in law mechanic and he has replaced the Idle Computer and the Idle Switch in the car. Still have the same problem.

Can someone give me a clue on what maybe the cause of this stalling? The car runs GREAT! It's just the stopping/stalling that gets frustrating. I really want to get this fixed. I don't want to bring it back to my brother in law without an idea on what the problem is. He'll just replace another part thinking that will fix it.

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Old 12-20-2002, 08:31 AM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Some times thats the problem with brother-in-law technicians. This is a technical industry and true diagnostics require specialists.

Proper idle will require proper every thing else. This definitely means timing. Bump it 5 degrees for good measure. The idle valve is controlled using pulse width modulation. This means that the valve which is naturally open is pulsed closed. The average voltage measured across the two connectors is a result of battery voltage being there some amount of the time. If battery voltage was 12v and the time was 50% the voltage would show 6v unless viewed with a scope. When viewed with a scope the /picture is a bunch of square waves at a given frequency with the duty-cycle being the changable commodity.

The actual figures that matter for the idle valve on your cars are milliamps current. Proper control should happen at about 6-700ma. If its not there the car should idle high. BTW check the unplugged idle valve for atleast 1800rpm as I have seen many of these cars with intentionally limited air passages (to fix the more common high idle problem).
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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