There is a sensor that tells EDS what the engine temp is, and by cold temps EDS increases idle until operating temp is reached.

 

Can you tell me where that sensor is located?

Thank you!

 

It is actually a thermister and should be located on the head driver side towards the rear.

 

First look on the firewall by your brake master CYL. Switch the ELR knob to position 7. See if things improve. Each position corresponds to a different idle speed.

If this doesn't improve the situation then you will need to adjust the idle speed set screw in the back of the injection pump.

 

I think the electronic idle switch is only on the older cars. Mine is a 1991 (non turbo, btw) and it doesn't have that switch. I have already increased it on the IP, but I can't go any higher, or the idle at warm temperature will be to high. That's my problem: it's only too low when it's still cold...

 

Curious if you made any headway on this. My 93 300sd is idling around 550, and when I let off the throttle fast it shoots low and bounces back, so down to 500 or so for a moment…

I need to pull codes - have you pulled codes?

I know the low idle is consistent with an unplugged EDS - my 91 350SD would idle low with the eds unplugged… but if plugged in, something else is wrong. Notionally pulling codes might help…

 

Curious if you made any headway on this. My 93 300sd is idling around 550, and when I let off the throttle fast it shoots low and bounces back, so down to 500 or so for a moment…

I need to pull codes - have you pulled codes?

I know the low idle is consistent with an unplugged EDS - my 91 350SD would idle low with the eds unplugged… but if plugged in, something else is wrong. Notionally pulling codes might help…

I have since resoldered the joints and replaced the capacitors on the ELR module, with no luck... I'm still trying to figure out some things, but I'll probably just try a replacement ELR module/relay. Today I'll check if the OVP relay is functioning properly, but I think it is since I don't have an ABS light and my tacho works.

 

How old is the OVP relay? If it is more than 10 years, a new OVP relay is a wise investment and keep the old one as a backup.

 

I have no idea, it's the one that was on the car when I bought it, about 1.5 years ago. It is the newer style, with two 10 Amp fuses, I don't know if that might be the original or if it has been replaced with a more recent one.

 

Check the manufacture date stamped on the relay. Also check the brand, OE MB/Striebel and KAE(hler) are acceptable. The rest is garbage.

 

This is the OVP relay I have. I did some testing directly with the car battery, by connecting battery positive to pin 30, and the negative to pin 31. That resulted in aproximatly 12V on both 31a pins, and no voltage anywhere else, which is correct. Than I took another lead from the battery positive to pin 15 (simulating ignition on), and I heard the solenoid clicking, but I only measure 12V on both 87E pins, but no voltage on both 87L pins. Is this correct, or is my OVP faulty?

 

Situation Update: By looking at ELR wiring diagrams (even though I only found diagrams for 7-pin OVP's, but I think it's similar for the 9-pin ones), I discovered that one of the 87L pins is directly conected to the Y22 solenoid on the IP, so I'm pretty confident that I found my problem. So I decided to open up the OVP relay (what a pain that was...), and I found what's in the picture below: one of the components seems to be burnt, and it even damaged the circuit board, giving me even more certanty that I found my problem (even though the relay is at least partially working). I tried to go over the solder joints, but it didn't solve the issue, because there's either a burnt component or the PCB is destroyed because of it. Next step is to get a new relay, and fingers crossed, I'll have electronically controlled idle!

 

One word. . . . TOAST. 1st step is getting a new OVP relay. Dollars to donuts that may be all that is needed.

 

Yup, I sure hope so! All this time I have been focusing on the ELR module, on which I had resoldered and replaced the capacitors, without any luck, and it was the OVP relay after all! I never suspected it because in most cases I have seen while researching the ABS light would turn on and the tachometer wouldn't work. I'm 95% sure this will fix the problem now, which makes me really happy because driving on these cold winter days will be much more confortable...

 

As I've stated hundreds of times before, the OVP relay is a wear and tear item. I replace mine with every other new battery, per advise given to me by a old MB dealer tech a long long time ago.

 

If your car is like my 91 W126, the temp sensor for the EDS is it's own single pin connection on the water outlet housing. There's another sensor there for the climate control. The sensor fo the glow plugs and dashboard display is on the side of the cylinder head.

-J

 

Another update: finally the OVP relay arrived, and was replaced. It did make a diference, but NOT for better!!! For some reason, the cold idle is even lower than before! In the morning it's at 490-500 rpm! I assume it finally allows current to get to the ELR/ARA module, as I think now the ARA is functional. Before, specially when cold, the car used to judder quite a bit when taking off in 1st gear, and now that seems much improved. When shutting off the engine, the idle increases slightly for a split second. It also seems that sometimes, if i revv it, it will hold around 600/650 rpm, and after a few seconds go back down to 500. Also when pulling codes with the OBD1 blinking code reader, in port number 4 (EDS system), my fault code number 6 (open/short circuit on ELR module) is now gone. It only gives me number 5 (related to the EGR, but my car doesn't have EGR, so I think I can ignore that), and a number 2 (fuel rack position sensor). With the engine running there are no codes at all, and I can't find any sensor connected to the injection pump, so I don't know what to make of code number 2...
In conclusion, changing the OVP relay definitely did something, but it still isn't right. I wonder if I just need to increase the idle mechanically on the ajustment screw behind the IP, but my idle seems correct when the engine is warm (around 650/700 rpm), so wouldn't that result in an overly high warm idle? I also tried measuring the voltage at the connector that goes into the ELR actuator, and sometimes it had virtually nothing, and other times I got values between 4 and 6V. Could it be a wiring issue in that cable? How could I test that properly?
Anyway, sorry for the very long text, and your help and advice is very much appreciated.

 

PROBLEM SOLVED!!! FINALLY!!! Well, after all this time (probably over a year dwelling on this issue), I have my ELR idle control working! After countless hours of research and testing with a multimeter at hand, the fix was ridiculous, it made me laugh, really. You know how there are 2 solenoids at the back of the IP? The ELR and the ARA (anti-jerk) solenoids: they both have identical two pin plugs. They were swapped around! I literally interchanged them, and boom! My cold idle went right up! Granted, the replacement of the OVP relay did take part on this solution, because the old one was indeed faulty. If anyone has a similar issue to mine, check that first, because it is the easiest thing to do... The plug with the shortest wire should be the one on top, and the longer one goes to the lower solenoid!

 

is the ARA for MT cars? I’m not familiar with it.

I’ve recently removed the IP on my 1991 350SD OM603, it only had the Y22.

I don’t see another on my w124 or 201.

Where on the IP is it on yours?

I know we are interacting on two threads now…. Since this one has the prior resolution perhaps you can share your other research? I’m not seeing voltage on pin 8 and have continuity to the temperature sensor.

 

Congrats! On my car, I simply unplugged the ELR and then turned up the idle speed screw so the hot idle was just a tad high.

 

You can test the system pretty easily by following the service manual. Maybe it's something simple like it was for me!

 

ARA magnet is bottom right.

ARA is for MT cars only.

 

Thanks!

That’s just a plate on the AT cars. Makes sense.

 

No, the 350 doesn't have the adjustable idle speed like the 300. It's set by the EDS and coolant temperature.

 

I was refering on the post above.

I believe the coolant temperature are only using the IPs with PLR pneumatic idle control.

The IPs of the OM 603 always have ELR !

Setting the idle on IPs with ELR goes like this : you fix the ground idle with the screw over the magnet on 570 U/min with no plug on the magnet. If you set the plug the idle should rise up to 640 U/min.

 

I thought the IPs are the same exept the control unit and the plug on top. I once mounted a EDS IP in my 300 TDT without EDS. I just left the plug on the pic alone and it worked perfect.

 

The control plug you’re showing with three pins is not the Y22.

There may well be other IPs that are set with a higher base idle and whatnot. The 616/617 cars didn’t have this and didn’t have any issues.

 

The EDS temp sensor isn't in the head, that one is used for the glow plug relay and the dashboard gauge. The EDS temp sensor is the single pin sensor in the upper water neck. The 2 pin one is used by the automatic climate control.

 

at least on the 601, there are two in the head. The FSM shows it, and I’ve confirmed it when diagnosing pin 8 of the N8 ELR relay. These photos aren’t great but you can tell the relative location based upon where the two sensors are next to parts of the IP.

The further back one is the gauge, the forward one is for the ELR pin 8.

The two red sensors are also there in the head.

The EPC confirms this is correct for at least the 601.

If they’re somehow combined on later 602/603 engines, Ok. Point is there are multiple ways these are set up from the factory.

Now if you’re telling me that the sensors are correct but the connections are incorrect, I’m interested. The location of B11/1 is hard to discern from the poor FSM photo.

 

You are right !

at 2 valve diesel: Sensor in the middle of the head = display in the dashboard + if necessary for pre-heating. There are 2 in the COOLING WATER OUTLET at the front of the head, with the 2 pole being for the air conditioning fan and the other for the ELR. Sensor waterpump: Temperature switch 50°C leads to the changeover valve pressure converter AT