M103 temperature sensor, 4 pin, fitment query

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Kenny124

New Member
Joined
Dec 5, 2018
Messages
19
Location
Falkirk
Car
W124 TE300
Some advice needed. I want to change the temperature sensor on my 1991 M103 engine. This is the 4 pin sensor which sends information to the injection system.
The wiring loom plug which fits onto the sensor has an internal 'flat' but the new sensor (and the one fitted to the car at the moment) has no lug or raised section to engage with this 'flat' therefore the plug will fit on the sensor in four different positions. Is this correct? Can I just fit the plug in any position and expect the sensor to work correctly?

Thanks !
 
IIRC the pins are paired diagonally, so it shouldn’t matter which way the plug goes on. There’s two sensors in one. Measure with a multimeter to confirm if you have one? :)
 
Hi Kenny,
I’m trying to remove this 4 pronged sensor from my father in-laws w124 m103
It’s very tricky and he’s worried about me break8ng more stuff on his car 😬 can you advise how to take it off? Cheers
 
Hi Kenny,
I’m trying to remove this 4 pronged sensor from my father in-laws w124 m103
It’s very tricky and he’s worried about me break8ng more stuff on his car 😬 can you advise how to take it off? Cheers
Do you mean the plug from the sensor or are you trying to remove the sensor itself?

The sensor just unscrews. Large hex on the brass body - deep socket required, probably not enough room for a spanner unless you remove other stuff first.
 
Hi Kenny,
I’m trying to remove this 4 pronged sensor from my father in-laws w124 m103
It’s very tricky and he’s worried about me break8ng more stuff on his car 😬 can you advise how to take it off? Cheers
I honestly can't remember how I did it - but I do remember it was fiddly and tight for space though. Sorry I can't help!
 
I honestly can't remember how I did it - but I do remember it was fiddly and tight for space though. Sorry I can't help
yeah there’s not much room, It’s got small lugs on the side like they need squeezing in, i suppose i’ll just have to keep fiddling with it. did you test your’s on the car?
 
The connectors pull upwards, it’s been ages since I took one off but pretty sure they just pull off.

Post a picture? :)
 
Before you get too far into it, what fault are you trying fix?
 
Before you get too far into it, what fault are you trying fix?
Morning,
We've had a real mission over 1 year it started here
Wouldn't fire, eventullay we replaced the rotor cap after we thought it was ok and moved on...which got it going, it then went straight into reving high @ 1500 and staying there.
If I unplug the icv it drops down to 550-700 and sounds ok, plug it in and it shoots up. it clicks when the ignition is turned on (I did a YouTube test) I replaced both vacuum pipes to and from icv, replaced the cps. I'm sure I've had the engine temp sensor off but unsure how to test it. TBH I haven't touched his Mb for months as I was at a loss and leaving the ICV unplugged has meant he has been able to drive it and get it through an MOT. I read a guy somewhere had leant in the air filter while trying to sort out the high idle issue Andy it made it settle back down so that's what I tried yesterday and it didn't make any difference.
Are we there yet;) sorry its soooo long and that's not even including the older threads!!
 
Morning,
We've had a real mission over 1 year it started here
Wouldn't fire, eventullay we replaced the rotor cap after we thought it was ok and moved on...which got it going, it then went straight into reving high @ 1500 and staying there.
If I unplug the icv it drops down to 550-700 and sounds ok, plug it in and it shoots up. it clicks when the ignition is turned on (I did a YouTube test) I replaced both vacuum pipes to and from icv, replaced the cps. I'm sure I've had the engine temp sensor off but unsure how to test it. TBH I haven't touched his Mb for months as I was at a loss and leaving the ICV unplugged has meant he has been able to drive it and get it through an MOT. I read a guy somewhere had leant in the air filter while trying to sort out the high idle issue Andy it made it settle back down so that's what I tried yesterday and it didn't make any difference.
Are we there yet;) sorry its soooo long and that's not even including the older threads!!
The temp sensor wont make it rev to 1500, without seeing it I would say you have vacuum leaks. "Leant in the air filter" means messing about with the mixture screw, which is otherwise know as the bodge screw (so called because every bodger cant help messing with it).

With the engine running, spray brake cleaner around every rubber hose and gasket you can see on the inlet manifold. If the revs pick up you have found a vacuum leak. The favorite places are the rubber boot under the metering head, and the injector sleeves.

The ICV sounds like it's working as the revs jump up when connected, there are other checks to do but try the brake cleaner test first before replacing anything else.
 
The temp sensor wont make it rev to 1500, without seeing it I would say you have vacuum leaks. "Leant in the air filter" means messing about with the mixture screw, which is otherwise know as the bodge screw (so called because every bodger cant help messing with it).

With the engine running, spray brake cleaner around every rubber hose and gasket you can see on the inlet manifold. If the revs pick up you have found a vacuum leak. The favorite places are the rubber boot under the metering head, and the injector sleeves.

The ICV sounds like it's working as the revs jump up when connected, there are other checks to do but try the brake cleaner test first before replacing anything else.
thanks for your reply,
if it’s reving high so would spraying b.cleaner make it run even higher?
i’ll try and make a video soonish
 
THE MOTORISED IDLE CONTROL VALVE IS ACTUATED BY THE ENGINE ECU DEPENDING ON VARIOUS INPUTS.

img105C.jpg
 
thanks for your reply,
if it’s reving high so would spraying b.cleaner make it run even higher?
i’ll try and make a video soonish
Yes, if the revs pick up the engine is sucking in the brake cleaner through a vacuum leak.
 
the signal to the idle valve is controlled by several inputs from various sensors so the short answer is no. a more likely candidate is the throttle valve switch which signals idle and full load throttle valve plate positions- if faulty its going to tell the ecu the throttle plate is closed even when open and open the ICV to compensate- might be worth disconnecting it as a test?
 

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