EHA Help needed
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1985 W124 230E
EHA Help needed
My 1985 230e started experiencing issues a few months ago with rough idle, rpms dropping after rev, running rough with ac on, etc. I started by testing the fuel pressure on the top half of the distributer (don't have the proper tool to test pressure on bottom half) and it was getting 80 PSI but slowly dropping after. Replaced the injectors, replaced fuel distributer boot cause it was torn, confirmed there were no vacuum leaks also replaced fuel pump check valve and fuel accumulator.
after doing that work the fuel pressure now holds around 40 psi when the engine is shutoff and maintains the 80 psi while running.
but I am still having the same issues as before and am beginning to think that its something to with the electrical because I just noticed that the eha valve connector was covered in oil so i tried to unplug it only to find that the car runs the same with it plugged in on not. I had also found the same thing with the idle switch on the throttle cable linkage, no matter if its pushed down or not or unplugged it just doesn't do anything.
if anyone with knowledge of this system can help me out it would be greatly appreciated and thank you
after doing that work the fuel pressure now holds around 40 psi when the engine is shutoff and maintains the 80 psi while running.
but I am still having the same issues as before and am beginning to think that its something to with the electrical because I just noticed that the eha valve connector was covered in oil so i tried to unplug it only to find that the car runs the same with it plugged in on not. I had also found the same thing with the idle switch on the throttle cable linkage, no matter if its pushed down or not or unplugged it just doesn't do anything.
if anyone with knowledge of this system can help me out it would be greatly appreciated and thank you
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From: SF Bay Area, CA
190E 2.6L 1989, 190E 2.6L 1988, BMW 535dXdrive 2014, BMW 428i 2015
Sure sounds like your ECU is non operational probably due to a busted OVP. Measure the voltage from pin 6 to pin 2 on the round X11 port next to your ignition control module.
I'm guessing it will measure 0V (should be battery voltage). If so, get a new OVP from your mercedes dealer and not a URO one. They last about 10-15 years depending on many factors.
From your description of the issues prepare to be dealing with multiple issues.
I'm guessing it will measure 0V (should be battery voltage). If so, get a new OVP from your mercedes dealer and not a URO one. They last about 10-15 years depending on many factors.
From your description of the issues prepare to be dealing with multiple issues.
MBWorld Fanatic!
Joined: Mar 2016
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From: SF Bay Area, CA
190E 2.6L 1989, 190E 2.6L 1988, BMW 535dXdrive 2014, BMW 428i 2015
Thread Starter
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1985 W124 230E
I'm a bit unfamiliar with testing the voltage on the icv, it's saying 0v but I'm sure I'm measuring wrong because the car seriously struggles to run without it plugged in so I'm going to assume the connection is good? The car (icv plugged in) idles at around 600-900rpm, rumbling around 500 after I let off gas at low speeds.
MBWorld Fanatic!
Joined: Mar 2016
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From: SF Bay Area, CA
190E 2.6L 1989, 190E 2.6L 1988, BMW 535dXdrive 2014, BMW 428i 2015
Sorry but you did not answer my question.
Please just respond to these questions line item by line item.
(1) What is the rpms with the car idling in park with the warm engine.
(2) What is the rpms when you unplug the IACV connector as the warm engine is running
(3) Measure the voltage on the connector after it was unplugged (DC voltage)
(4) As the car is still running plug in the IACV connector and tell us what happened. Did the engine stall?
Cheers!
Please just respond to these questions line item by line item.
(1) What is the rpms with the car idling in park with the warm engine.
(2) What is the rpms when you unplug the IACV connector as the warm engine is running
(3) Measure the voltage on the connector after it was unplugged (DC voltage)
(4) As the car is still running plug in the IACV connector and tell us what happened. Did the engine stall?
Cheers!
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1985 W124 230E
Alright! Here's what I found!
(1) Idle RPM in park is 800 (warm engine)
(2) The RPM when IACV is unplugged (warm engine) is 500
(3) When I measured voltage pin to pin, I got 0v. From ground to pin it doesn't get a good read, randomly fluctuates so I don't have a solid number.
(4) While running, when I plug the IACV connector back in the idle increases to 1000 RPM and stabilizes for a few moments before returning to 800rpm rough again.
Hope my answer's gave a better idea, Thank you!
(1) Idle RPM in park is 800 (warm engine)
(2) The RPM when IACV is unplugged (warm engine) is 500
(3) When I measured voltage pin to pin, I got 0v. From ground to pin it doesn't get a good read, randomly fluctuates so I don't have a solid number.
(4) While running, when I plug the IACV connector back in the idle increases to 1000 RPM and stabilizes for a few moments before returning to 800rpm rough again.
Hope my answer's gave a better idea, Thank you!
Last edited by mikithagoat; May 11, 2026 at 01:59 PM.
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MBWorld Fanatic!
Joined: Mar 2016
Posts: 1,369
Likes: 195
From: SF Bay Area, CA
190E 2.6L 1989, 190E 2.6L 1988, BMW 535dXdrive 2014, BMW 428i 2015
That is certainly the opposite of what should be happening. When you unplug the IACV connector the rpm's should increase not decrease. So you have multiple issues here.
But your readings suggest the ECU is alive and trying to regulate the idle to the best of it's capabiilty.
Does your CEL even work and is it lit up?
If not you need to try and read some error codes on your diagnostic port by the battery. You need an OBD-1 reader (if it is not built in, some models have it built in)
I would start by measuring your duty cycle at the X11 port pin 3 to pin 2. Read up on this and the possible error codes it may have. It should be cycling at ~50% duty cycle +/-5% every 1-2 seconds
But your readings suggest the ECU is alive and trying to regulate the idle to the best of it's capabiilty.
Does your CEL even work and is it lit up?
If not you need to try and read some error codes on your diagnostic port by the battery. You need an OBD-1 reader (if it is not built in, some models have it built in)
I would start by measuring your duty cycle at the X11 port pin 3 to pin 2. Read up on this and the possible error codes it may have. It should be cycling at ~50% duty cycle +/-5% every 1-2 seconds
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