I'm having an acceleration problem and occasional rough idle in my 87 300E. The car will go totally listless with little to no power at all under normal acceleration. If I totally step on the gas and open the throttle all the way, it will take off like it should but for 2-3 seconds, it acts like it just isn't going to go.

I've checked the plugs, distributor and rotor, wires, etc. and nothing has changed. I've seen several threads about air flow sensor problems, O2 sensor, throttle actuators, etc. Which all seem to be possibilities.

What I'm trying to do before I throw parts at this thing is to check the codes. I can't figure this out. I see Arthur Dalton's homemade tool to check the flashes, but where are the pins on my car??? The only thing I can find is on the drivers side fender, a small round deal with 9 pins. Is this it? The banana plugs indicated from Arthur don't fit in this thing (too big) so I'm thinking this isn't it?

Any help would really be appreciated.

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Ty H.
'87 300E 135K Miles

No, there was a squarish bock on the passenger side, but I think it was only for the later W124 models that have Bosch HFM injection. Yours has the K-jetronic with the airflow sensing plate and fuel distributor.

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Prost!

Thanks. I'm going to check out the info on the mechanical injection.

I just talked to a local MB guy who said my problem is almost certainly a bad EHA valve. After reading up on it, it does make sense. We'll see...

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Ty H.
'87 300E 135K Miles

I fixed the link to the HFM document where you can see the square diagnosis port with the LED (page 11/7).

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Prost!

<< I see Arthur Dalton's homemade tool to check the flashes, but where are the pins on my car??? The only thing I can find is on the drivers side fender, a small round deal with 9 pins>>>

Your chassis does not have Led Flash Format code retrieve or Led DM .
It has Duty Cycle and requires a DMM capable of reading Duty cycle %.
That is where you use the 9 pin Diagnostic port.

Search "Duty Cycle"

Page 13: 9 pin.

http://www.autolib.diakom.ru/CARS2/pribor/cs1000/manual/cs1000_mb.pdf

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A Dalton

Ok. Thanks for the info. Hopefully the EHA fixes the problem. It's a pricey little part...

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Ty H.
'87 300E 135K Miles

i just purchased a working used one for $60.00 due to its extremely high cost,but i found out as easy as it is to replace,the air/fuel ratio and idle speed need to be altered to calibrate the new eha valve to your computer,its not easy.

$60 is a bargain based on what I've seen. Was that on ebay?

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Ty H.
'87 300E 135K Miles

So I stumbled on a good eha valve from a junk yard for $20 bucks. The employee behind the counter had no idea of the value of the part. The owner was ticked when he overheard the final sale but let it go since his guy had already made the deal!

But...it didn't solve my problem... Over the last few months, the intermittent rough idle has become more consistent. Not sure where to go next... Plugs, wires, cap and rotor are all fine. I did take the idle valve off and clean it, but not totally thoroughly. Not sure if it should be replaced or what.

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Ty H.
'87 300E 135K Miles

Your 87 does not have a diagnostic, only an O2 sensor light.

Check all your idle air hoses for cracks. If they are hard or have not been replaced by you since owning the car, replace them. Get them from the dealer, not online. Trust me. I replaced all mine with URO aftermarket and they cracked within a year. I had a thread about why my 260E was not starting.

Last time fuel filter was replaced?

Pull back the passenger carpet and probe the O2 sensor connector to see what you are 'really' running for duty cycle. If you receive a slow output, or none at all your O2 sensor could be toast.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
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FWIW, early W124s with KE-Jetronic had the 8-pin square diagnostic connector block beginning in 1988 on California version cars (federal versions may have started at the same time), but only the California versions came with the pushbutton and red LED to check for flashes without requiring the homemade reader.

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1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't

Correct. My 88 300TE California has the diagnostic connector while my 87 California does not. 88 Was the year which gave the codes.

OP: Have you replaced the OVP yet?

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

im having a similiar issue with my 89 300ce,i had to replace the eha, fuel pumps and the o2 sensor,i also had to replace the fuel filter,check your ovp also

Update: so I did replace the EHA. I do not have any problem with acceleration after doing that. However, I still have a rough idle.

I haven't done anything with the OVP.

I've also heard there is some adjustment that can be made to the EHA? I haven't done anything with that. Could have that anything to do with the idle?

BTW, after new plugs, wires, fuel filter and O2 sensor I'm getting noticeably better mileage.

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Ty H.
'87 300E 135K Miles

You can adjust the EHA via a small screw in the rear. MARK THE ORIGINAL POSITION.
Without use of a fuel pressure gauge you have no way to correctly adjust it. Mark the original position and give it turns in 1/8th's.
FYI Though: I HIGHLY doubt that is the cause of the rough idle though. Look at vacuum leaks at the idle control valve.

What does your economy gauge show at idle? Where is it at? Does it fluctuate at all?

Does the engine smooth out in neutral? Condition of motor mounts?
Is your ABS light illuminated? (OVP failure symptom)

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k