Not sure which sensors are required to start/idle.

I know the normal sequence of things to start the engine when the key is turned is this:

1. SOV opens (click sound)
2. ECU cycles rack full on ("tok" sound) and should drop back to a position about 6mm forward of "closed" or full aft. This is the idle position. 1 and 2 may occur simultaneously.
3. During cranking, the ECU will slowly advance the rack forward/more fuel until it senses the engine has started. Once it senses the engine start, it will instantly drop the throttle back and maintain idle.

That's the way it SHOULD work.

This is a good reason to remove the side cover so you can observe the rack movement during start up. It's also a good excuse to replace the gasket on the side cover...

__________________
-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

Replaced the upper engine wiring harness and all is well!
I can't quite believe it but I've tested the old harness and whilst there is not shorting between the pins I found two non conductive connections to what I think is a temp sensor! I have the OM606 non turbo and the sensor in question has 4 pins and is located on the back right side of the head.
I can't find any other fault with the loom so can only assume that these two bad connections were causing the ECU to tell the IP to run on full throttle???
This could have been really dangerous had this happened whilst driving.
I've attached an image of the sensor location (the one wrapped in grey tape was the problem sensor). Could any one confirm that this is a temp sensor??

Attached Thumbnails

 

Not sure if I should post a new thread so please advise if I should....
I've solved the runaway problem and now the car starts and idles ok for a short while then the idle becomes a little erratic.
I've scanned the car and have errors with the ICS (I think this is the Idle control switch?) so I'm guessing that's why there is a problem with the idle? , a stop light error and an air intake temp sensor error. The air intake temp sensor was missing when I got the car so I know this needs replacing! Where should I start looking for the stop light error? Could this just be a bulb replacement?

I'm getting a reading for the RPM but the tachometer isn't registering anything.
The heating is also blowing hot even when on a cold setting.
The Coolant temp on the instrument panel is rather hit and miss and seems normal then shoots right up and then returns to normal.
Could the ICS and tachometer be connected on the same fuse? If so does anyone know where I should start looking to try and fix this?
Thanks in advance

Start looking for ground problems if you have several unrelated symptoms. The brake light is likely a bulb or socket and might not have anything to do with the other symptoms.

__________________

Gone to the dark side

- Jeff

These cars are notorious for the brake pedal switch failing.

There are two contacts in the switch, one makes when the pedal is pushed (and the pin extends), this turns on the brake lights
The second contact breaks when the pedal is pushed. This goes to the ECU and prohibits more than idle power while the contact is broken.

Easy peasy to change out and not too expensive.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Thanks again for all the help guys. I don't have a lot of experience with Mercedes so the experience of the people on here is a massive help.
Whilst checking the fuses I found that someone had used the wrong fuse in the fuse board beside the battery (under the rear seat). Position 7 should have been a 7.5 but someone had use a 4 and it had blown! Changed it and I've got my tachometer back! Nothing I've researched online or on the fuse holder guides says that this fuse should be related to the tachometer!
So I've still got a rough idle (starts and idles fine at first but then surges a bit). Anyone know where the ICS (Idle control sensor) lives on these cars??
Also the heater is still blowing hot air when on full cold! Anyone got any idea's where to look for problems here? I'm reluctant to think it would just be low refrigerant in the A/C as surely that wouldn't cause the air to be hot but hey ho this car has a mind of it's own so guess I can't rule that out!

Oh I've noticed that I've got a vacuum line that's not connected anywhere! If I suck on it it opens the butterfly valve on the air intake. It's about a meter and a half long so could connect to almost anywhere in the engine bay!! It is connected at one end to something under the expansion tank but I've no idea where the other end is supposed to connect. I can't see anywhere obvious where this should be but perhaps that's causing my idle issue.

That sounds like the resonance butterfly used to vary the length of the intake, if so there is a valve block linking the two together (two butterfly valves).

On the OM606 fitted to the W124 it's bolted to the underside of the intake manifold.

Regarding the erratic idle, re-attach the five earth points under the hood.

These can rust and give all sorts of issues, give me a shout if you need the location points - fairly easy to spot as small clusters of brown wires held with a single bolt to the tin.

__________________
David


1996 Mercedes S124 E300TD - 129k - rolling restoration project -

1998 Mercedes W210 300TD - 118k (assimilated into above vehicle)

Sorry, didn't see babymog's post suggesting earth points too.

__________________
David


1996 Mercedes S124 E300TD - 129k - rolling restoration project -

1998 Mercedes W210 300TD - 118k (assimilated into above vehicle)

Take a picture of the starting point of this unhooked vacuum tube and I'll see if I can't find it on my car and trace where it goes.