Hello. I have an issue on my w124 1988 300ce. I was at the drive thru last week and I started to get rough idle, ABS light turned on, and my blower motor shut off, when I gave the car throttle, the issue went away, when I stepped on the brake pedal the problem came back. I quickly deduced it was lack of voltage so I turned off the lights and made it home. Tried starting the car right back up again, and no go. Jump started it and checked the voltage at the battery and I had a very slow but steady drop, at 3/4 throttle I'm getting no more than 12.9 Volts peak. Thought it was the alternator, bought a new one, installed it, same issue. Battery is new. What can it be? The infamous OVP?

I've had the rough idle come and go for a bit now, same with the ABS light, car shut off at a light once when I came to a stop. Started right up again. Haven't really had problems with a rough start.

Thanks a lot for the help.

Check the ground strap on the bellhousing.

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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff

Check all earth connections remove them clean up the area it contacts and grease it. Then put the earth straps back on Then look for ant vacuum lines that may be loose ,look at the rubber elbows for cracking .

Check that OVP out ,and look at the fuses on the top ,give it a shake is it making a noise when you do? if it is its shot..Another is regulator in alternator ,brushes worn out easy fix this one .

At least on my 1990's 124's and 129, when that dang ABS light comes on out of the blue, accompanied by a rough idle, the OVP is the first thing I suspect. I pull out a pre-tested OVP from my "never get stranded" emergency parts kit in a water tight box in my trunk and plug it in.

Do the same and see what happens. The next I suspect is the MAS relay in my cars, in your vintage car, you have three different relays to check and swap good ones in with.

Checking the ground strap is a good thing to do regardless (though unless you are running around without an engine splash tray or live in an area where they salt the roads, probably not the cause).

Make sure to let us know what you found.

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03 CLK430 Cabrio 211K Pweter Silver/ Oyster Leather
90 300SEL 214k Pearl Black/ Alto Grey/Black Leather

Prior: 85 190E, 88 300TE, 89 300TE, 90 300E 2.6, 90 300TE, 92 300E 2.6, 91 and 93 300SL, 87 Ferrari Mondial Cabrio

I know you just replaced the alternator but what about the voltage regulator on the alternator? Its likely that or the OVP as was previously mentioned.

Does the battery light come on in the dash? If not, the problem...believe it or not...is the bulb. If the idiot light in the dash is bad, the alternator will never charge.

ahhh haaa! so bought this 92 300e the other day and ran it around (before, during and after purchase) for a bout 2.5 hours. only thing i noticed was a mild stumble once or twice but that was it. didn't use it yesterday but did
start it to see if battery was holding charge.
today i start it (raining since yesterday) and warm it up for 10 minutes and everything is fine. pull out of the drive and it stumbles hard but then goes another 1/4 mile and dies. try to start and nothing, but the tach needle jumps up to 5k rpm when i turn the key. go back an hour later and it starts up and makes it home.
now i can start it and it runs for 2-3 minutes before the abs light comes on and the blower comes on (climate control is set to 'off') and it dies.... plus the power seat doesn't work when this happens and the battery acts as if it's dead.
wait for 10-15 min and car turns over fine and starts but then the abs light comes on after a few mins and it dies....
is it possible the ovp is getting damp due to the 2 days of constant rain? or is some other gremlin at work??

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0o==o0

James 4:8

"...let us put aside the blindness of mind of those who can conceive of nothing higher than what is known through the senses"
-Saint Gregory Palamas, ---Discourse on the Holy Transfiguration of Our Lord God and Savior Jesus Christ


Centrally located in North East Central Pa.