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  #1  
Old 07-19-2004, 08:36 PM
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Join Date: Jul 2004
Location: Ridgecrest, CA
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1987 300SDL Idle problems

Hello All;
First time posting here, the folks at mbz.org sent me this way when I asked about their listserve...

Anyway, as the title says I've got a 1987 300SDL with about 206K miles on it. I live in the high dessert of Cal., lately it's been about 100-105F ambient, lots of sun.
I'm having a couple of problems, maybe three and they may be related, maybe not. I did some searching on the forums today and couldn't find anything that seemed to help so I thought I'd ask if anyone else has experienced these issues, here goes;

1) Sometimes when the car is first started during the day the idle will surge at first, it then returns to the normal 600 rpm. It used to be infrequent but now it's happening more and more according to my wife, who is the main driver.

2) Next issue. When returning from down south this last weekend we had a couple of instances where the rpm gauge stopped working and the a/c cut out as well. We stopped so that I could check the fuses, I found nothing wrong with them. After few minutes we started up the car and everything worked ok. About 20 minutes later the same thing happened again, but we were 20 minutes from so we continued on in the 105F heat (but it's a dry heat, as everyone says...). The first time it happened at a stop light, the second time it happened we were going about 65 mph. It seemed like the engine rpms fell a bit when the gauge stopped working but this is most probably my mental reaction to something not working. To compound matters, my wife tells me that this has been happening over the last few weeks, but she's never mentioned it since most of her trips are short and she doesn't use the a/c for those trips anyway.

So, that's what's going on. Has anyone ever had this happen to thier benz? Does it sound like there's a relation between the two problems? Any suggestions for fixing either issue would be greatly appreciated.

Thanks in advance,

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Old 07-19-2004, 09:38 PM
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Yes

they are related.

OVP relay is the prob.

Fairly inexpensive.

Cheers

Bernie
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  #3  
Old 07-19-2004, 11:28 PM
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Location: Eastern TN
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Just to explain, the AC compressor relay has a circuit that compares compressor rpm to engine rpm. If there is a discrepancy, the relay assumes the compressor is dragging and cuts the clutch so as not to compromise the belt and water pump.

And you get today's installment of 86-87 MB Diesels and electronics - losing electronics won't strand you. Don't fear the sixth cylinder.

Sixto
95 S420
87 300SDL

Last edited by sixto; 07-19-2004 at 11:53 PM.
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Old 07-19-2004, 11:38 PM
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Thanks, Bernie

Where is it located on the '87 300SDL? is there a MB part #?

I really appreciate the quick response,
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Old 07-19-2004, 11:58 PM
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It's the box about 1" by 1" by 2" deep on the engine side of the wirewall ahead of the driver. It's usually a silver box with red top and a clear plastic lid over a blade type fuse. FastLane has a picture of it.

It can also be a faulty connection at the flywheel rpm sensor or a faulty flywheel rpm sensor.

Sixto
95 S420
87 300SDL
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Old 07-19-2004, 11:59 PM
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I beleive it's in the relay box by the fuse box, but I'm not sure. IT's the one with a fuse on top under a plastic cover. I'd check the fuse, too, they corrode.

Wonder if my "funny idle" is also the OVP on my 300D -- I replaced the OVP on the 300TE chasing down an idle problem (the old one was OK), so I have a spare.

New relay should fix both problems.

Peter
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Old 07-20-2004, 12:00 AM
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Here's the pic from FastLane. Hope they don't mind.
Attached Thumbnails
1987 300SDL Idle problems-p205618124.jpg  
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Old 07-20-2004, 12:22 AM
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thanks all, I managed to find it just before it got dark here. I got the number and probably will make the order, plus a bunch of other stuff, tonight. I'll let you all know how things turn out.

thanks,
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Old 07-20-2004, 12:55 AM
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peragro,

Welcome to the forum. I am also from Ridgecrest. What a small world!
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Old 07-20-2004, 01:10 AM
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Definatly a small world, I'm sure that I've seen you driving around town. I'm (usually my wife and kids) in the white 300SDL.
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Old 07-20-2004, 10:08 AM
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You may have the only 300SDL in town, and I think I saw a white one running around. It must have been yours. Mine is an anthracite grey 1984 300SD which is usually mostly for commuting to work at the Lake.

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