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Old 02-08-2001, 11:26 AM
Artie Stringer
Posts: n/a

I have been chasing a warm up idle speed problem in my 1985 500SE. This has been hampered by the absence of a definitive wiring diagram. Local dealer supplied diagram of CIS-E; which does not match my setup.

The problem is low erratic idle with stumbles and stalls; which occurs after a problem free startup and when the temp gauge shows 40degs c to 60degs c. At approx 60degs c idle speed rises to a smooth idle as if a switch had been thrown.

Could someone give me the location of the coolant temp. sensor on this model and the expected electrical resistance.

Artie Stringer

1985 500SE

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Old 02-08-2001, 08:58 PM
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Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
There are two or three on top of the engine. I would think that the warm up regulator may be failing.
Donnie Drummonds
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Old 02-12-2001, 12:44 AM
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Join Date: May 1999
Location: New Location: VA Palo Alto HEALTH CARE SERVICES
Posts: 109
Warm up regulator

Would you please tell us where is this part exactly located in 88 420 SEL ?
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Old 02-13-2001, 09:57 AM
Artie Stringer
Posts: n/a

thanks for the reply. Two questions on the control pressure regulator - is the control pressure regulator user serviceable or is replacement with new the only option? Second; is the replacement of the regulator just a screw in operation or are there pressure adjustments to be made?

Thank in advance.
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Old 02-13-2001, 03:02 PM
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Join Date: Feb 2001
Location: BC, Canada
Posts: 378
It was mentioned that there are two or three such
sensors on the intake manifold. How do you identify
them and whether they are working? You shouldn't
have to replace them all together, should you?

1967 250SL
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Old 02-13-2001, 03:24 PM
Artie Stringer
Posts: n/a

For what its worth on my 1985 500se I have found what appear to be two electrical/thermal sensors. One is at the front of the L/H inlet manifold and judging by the w & g markings this is the thermal-time switch which controls the cold start injector. This can be tested for continuity on a cold engine and then for O/C on a warm or hot engine. One of the poles of the switch should show continuity to ground with the engine cold. Sort time after startup this pole should open and remain open on a hot engine.

The other is at the rear of the R/H inlet manifold and I suspect that this is the engine coolant thermal sensor, but I'm not sure. If the resistance/temp characteristics were known then this could also be tested easily with a multimeter using the resistance measurement function.

If you find any more info on these or other sensors please post.


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