Heres my problem.

**before the problem started I had the car stall once or twice shortly after starting and the car seems a bit underpower. The power range is now equal across the RPM range. Seems kinda weak around the low and mid RPM range.


1983 380SL (43,000 miles) suddenly developed a high idle condition. It now idles at approx 1,500 rpms hot or cold. I checked the idle speed valve and it functions (applied voltage to it and engine RPM dropped and stalled). Car restarted fine after test but went to high idle again.

I checked the fuse on the over voltage relay and its fine. I disconnected the idle speed computer - no difference. I also disconnected the Lambda control module - no difference in starting and idling.

I reconnected all modules and no difference. I tapped on over voltage relay and the idle jumped up a bit then slowed down to approx 900 rpms. Tap on the relay again, and RPMS go up to 1,500 again. Tap some more, RPMS start to "hunt" around. When the car settles down to about 900 rpms, and I remove the plug on the idle air valve, RPMS jump to 1,500 - reconnect the plug and they drop.

Since both the idle and lambda control get thier power feed from the over voltage relay, could the relay be my problem (this explains the high idle and lack of performance) OR is my over voltage relay, idle control computer and lambda control have gone south?

The previous owners hardly used the car and installed one of the battery cut off switches to keep the battery from running down when it was stored in the garage for long periods. The car did have many jumpings in the past due to dead batteries.

Thanks in advance!!!

-Kevin



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1990 300CE-24
1995 Jeep Wrangler
1995 Ford Thunderbird

Despite its fancy name the overvoltage protection relay is basically for your purposes just a power supply relay. Since it would kill the Lambda control module I would verify that the frequency valve is buzzing (this is a device that looks like an electric injector, it sits longitudinally beside the airflow meter on the drivers side). This will confirm that the control unit is powered. If it it is powered then the likelyhood is that the idle control unit also is being powered.

The idle control units are bad about cold solder joints on the PC board. We fix 3 out of 4 that are bad by resoldering the PC board. BTW both sides of the idle valve are connected to the controller. Any power at either side would indicate that the controller is being powered.


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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

[This message has been edited by Webmaster (edited 03-14-2000).]

I agree with Steve. I would replace the relay and see what happens. Then check the idle control unit if the idle is still weird. If you tapped on it and made it change, I think you found your problem.

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Benzmac:
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

WOOHOO! Houston we have lift off!

I doubled checked the wiring and followed the test proceed from the CD manual. Found that indeed I was not getting any voltage to the Lambda control and Idle Speed Control Computer. If I tapped on the relay I was get spikes of voltage and nothing more. The voltage wouldn't stay constant.

I put in a new Over Voltage Protection Relay and she prrrrr's like a kitten now. Engine fired right up, after a few minutes of running the idle dropped down and she ran real smooth. Not that it didnt run smooth before, but now you hardly know its running....no stray vibrations.

Also the pulling power under acceleration is back. The engine pulls strong and smooth. Before I changed the relay it felt like a bad miss on one of the cylinders. Now if I blip the throttle it takes off like I remeber when it was new.

A friend of mine bought this car from a family I used to work for. I still remeber the day they got the car new....I wasn't allowed to touch it (didn't have my licence yet). After 17 years they decided to part with it, never hit or painted. Interior and exterior has very little if no wear at all. The car has always been pampered. It had only seen about 2,000 miles in the past 3 years. My friend was able to get it for a 12,000. Good deal if you ask me.

Oh well....enough rambling on.

Thanks for advice...two thumbs up!

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1990 300CE-24
1995 Jeep Wrangler
1995 Ford Thunderbird

I am experiencing the same problem with my 1982 380SL, where is that voltage protection relay and what would be the correct part number?

Thanks to any who can help....