Just figured out that The tach counts engine speed signals and divides by 3 for a six cylinder m103 and by 2 for a four cylinder m102. So mine is showing 500. The real value is 500x3/2= 750 which is correct i suppose.
Correct. Like I was saying back in post 4. That is why your idle feels normal. At 500 rpm you will barely build enough vacuum for that gauge to peg and the idle will be miserably rough for a 4 cylinder engine.
So you can just do the math mentally with the RPM for now and chase other issues. I still stand by the OVP suspicion.
Ovp is checked good. I swapped 3 ovp s. The car run perfect now after the workaround i did by hooking the idle contact wire to the decel microswitch. I need sometime to decide when to change the throttle body as i ll need to remove all the ke jet assembly and the rubber boot wont stand a chance for not breaking.
I will upload a video tomorrow showing how things are working perfectly since cold start till warm engine.
I was checking on the internet and found out that the throttle position sensor is available in some stores. can this be accessed and replaced without removing the Airflow meter assembly?
my previous thought was that I need to replace the throttle valve complete assembly which is a bunch of items to be removed.
Yes you can just replace the AFM pot but don't bother with a far east no name replica. It will give you more trouble than your original (I heard
And the bosch ones are rather expensive.
What is leading you to believe you need a new one?
Mine is original in the car. 200K miles and very little sign of wear.
it is not the AFM I m talking about. I mean the Throttle valve Switch mounted to the butterfly valve that has Idle Contact and WOT contact. the switch is completely dead. as I stated above once I grounded the idle contact in that switch, the problem was solved. it seems that I can replace the switch only but I m not sure if it could be done without removing the AFM assembly. here is a photo of the Switch in question:
Sorry, I misunderstood. Not sure if you can just replace that 3 position switch by itself.
They do last a long time too. Mine is original at 200K miles for that as well. So not exactly a wear item either but it seems yours has malfunctioned.
Mine has not failed yet so I did not even know that there is a throttle closed position switch. Seems redundant since there already is a micro-switch. I thought it was just WOT.
I'll need to have a look at mine at some point.
yeah, I exactly questioned myself why is there a throttle switch + a microswitch. as the workaround I did was using the microswitch to achieve the throttle closed function. I even noticed that wiring from the microswitch goes to a different pin to the ECU but well I shorted both ECU inputs together at the microswitch and this didn't cause any problem. what I can tell that when using the microswitch for this function it is very sensitive, once you touch the pedal you feel the engine idle changing even before you open the throttle. I guess the throttle switch isn't that sensitive and may have some travel distance before closing and opening.
Also, I guess that now I understand why I was getting a sort of pinging on WOT and high loads. I m pretty sure that it is because of the WOT function not being achieved by the dead switch. speaking to wear items this car has done over 1 million kilometers "the odometer has completed one cycle and started another one " using 2 engines but with the same injection components! it was taken out from the old engine and put into the replacement one during car life. the car is well maintained by me and everything works like a charm. it just needs some minor body works.
That is a lot of Kilometers!
Since they are sold on line and not that expensive I would recommend replacing it instead of rigging it like you had to ingeniously.
If the two functions could have been combined Mercedes would have done it I suppose.
Yes the microswitch activates after the throttle plate is closed and seems the intent is to sense if your foot is on the as pedal at all.
The throttle switch on the other hand seems to try and actually sense if the throttle plate is actually fully closed.
On the M103 at least (depending on the white roller bushing's wear) there is a good 5mm-8mm difference between the two.
M102 linkage is different (vertical).
Exactly. I have learned that the two switches are used in order to smooth out the transition between idle and partially opened throttle. They create a sort of hysteresis. I did my workaraound just as a temporary fix as the replacement is a pain, i need to remove all the airflow meter assembly and make sure i have all rubber fittings that may break during removal due to the huge mileage of the car.
Correct, the switch is bolted on the outside with two adjustable bolts but you can barely see it. It s hidden by the intake manifold and the Airflow meter assembly. I guess it is impossible to access without the removal(at least on the m102). I ll try to take some pictures today and confirm if it can be removed or not.
The "Microswitch" is in the throttle linkage nest and should be easy to see with the air cleaner off.
The "Throttle Position Switch" is located at the end of the throttle butterfly valve shaft - opposite end as the linkage attachment - and is more difficult to see on most models. (And may require removing the fuel meter if you have to replace it. Thank you Mercedes for the great "maintenance engineering"!)
The microswitch tells the KE controller to interrupt fuel flow when you lift completely off the throttle (and there is about a two-second delay built into the controller electronics) and resumes fuel flow when you step back on the throttle. By resuming fuel flow before the throttle valve actually begins to open, the typical "jerkiness" of single switch systems is eliminated making the transition back to fuel flow seamlessly. And the fuel flow interruption delay eliminates any jerkiness if you quickly transition between off and on throttle multiple times in quick succession - what the tech literature on the system refers to as "hysteresis". ("Engineered like no other car in the world", remember!)
The TPS sends an idle signal to both the KE-Jetronic controller and the EZL ignition module to tell the KE controller to go into idle speed control mode and the EZL to fix timing at the programmed idle speed setting (see emission decal for that setting.)
The TPS can get dirty/sticky and not send the idle signal, which will cause uncontrolled high idle speed. This is often overlooked as a cause of high idle speed. (It's not always the OVP relay!) Often just a good exterior cleaning of the switch and shaft will restore function.
here s a picture where i indicated the switch location:
Hello Again, so I managed to get a used good throttle valve including a good working switch at a good price. but before I do the job I just wanna make sure if someone can confirm if any adjustments will be needed after the replacement. I have heard about the throttle stop screw that shall not be disturbed as it is hard to adjust.
I'll be doing the job myself since I don't trust any mechanic over the country so better to know what s waiting for me there.
Another option is to use industrial microswitches and installing them externally on the throttle linkage so they can achieve the same smooth operation without having to disassemble the old stuff.
So i was speaking to a mechanic and he affirmed to me that he never changed a throttle valve seperately. He always change the complete assembly with the AFM as the adjustment will never be same as factory. I guess i m goin with my own engineering way now using some industrial limit switches
BenzWorld.org forum is one of the largest Mercedes-Benz owner websites offering the most comprehensive collection of Mercedes-Benz information anywhere in the world. The site includes MB Forums, News, Galleries, Publications, Classifieds, Events and much more!