300SE High Idle Problem/Check Engine Light

Feb 20, 2006 | 07:22 PM

bob15489

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300SE High Idle Problem/Check Engine Light

My 1991 300SE has the check engine light on and is having an idle problem. I'm totally new to MB vehicles but I am pretty technically competent (extensive experience with turbo 4 cylinders and carburated V-8s). I'm assuming the light and the idle problem correlate as they pretty much both started happening at the same time. The idle in P goes up around 2k RPM, especially when it's hot. Does anybody have any experience with this problem and also how to read the codes out of the ECU? Thanks!

Feb 21, 2006 | 04:11 PM

BENZITCH

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From: Mercerville New Jersey

1991 560SEC Teal 1989 420SEL Ice Blue 1984 500SEC White

Idle Problem/Check Engine Light

There is an overload voltage regulator. It is most likey on the firewall on the other side of the break booster. It has a red fuse in the top. Try replacing the fuse first, if that is not it you might have some soder joint cracks in the OVR unit.
Bruce
BENZITCH

Feb 21, 2006 | 06:51 PM

bob15489

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The fuse appeared to be intact, however, I replaced it anyway. This did not solve the problem. I've read on some other threads about the idle control valve and similar issues. Also, how would I read the codes out of the ECU?

Feb 24, 2006 | 01:53 AM

darky_minded

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From: jed

cl600

i had the same problem i just changed the overload voltage regulator and all my problem were gone

Feb 24, 2006 | 02:07 AM

bob15489

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Ok, I'll try to replace the regulator and see if that fixes the problem. Is that a part I will have to buy from a dealer or can I get it at any auto parts stores?

Feb 24, 2006 | 02:15 AM

darky_minded

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From: jed

cl600

u get it from the dealer or you can get a used one to

Feb 24, 2006 | 02:27 AM

bob15489

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Just to clarify to make sure I get the right part, this is seperate from the regular voltage regulator? Also, out of curiosity, what exactly does the overload voltage regulator do?

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Feb 24, 2006 | 08:46 PM

bob15489

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Ok...I got the new overload relay from my local MB dealer and swapped it. I also disconnected the battery for about 20 mins to reset the ECU. The check engine light came back on after the car was running for about 1-2 minutes. The idle is significantly lower now but still high (idles around 1300-1400). Before I start replaced other sensors (like the idle control vavle) I would like to pull the codes out of the ECU. Where would I connect the leads for the LED and is there a website out there that has a list of the different codes?