Throttle Body
 

Am looking for an explanation as to the function of the "Throttle Body". What would be some typical symptoms when this component fails?

On a 124 Body, is that an expensive part? is it a DIY?


Thanks

Phil

Diesel engines to not have a throttle body, only gas engines as they are "throttled" and diesels aren't.

The throttle controls the air flow by closing off the intake with a butterfly valve. The casting the butterfly valve is in is called the throttle body, and can only fail by wear on the shaft or sides, or in the case of the new electronically operated "drive by wire" systems, the actuator not moving correctly.

K-Jetronic fuel injection systems also have a mass air flow sensor with a plate in a venturi, but it is not a throttle.

What model and engine?

Peter

Peter,

The reason I was asking about the "Throttle Body" is that I was corresponding by E-mail with another guy that has the Identical car as mine i.e.: a '95 E300 Diesel OM606 Engine, and has had to replace the wiring harness. I also have a problem with the wiring harness that I fixed temporarily but that eventually I also would have to replace.

But back to the "Throttle body". His Mercedes dealer told him that when they replace a wiring harness on that car they usually also replace the "Throttle Body". He chose to have the work done by an Independent Garage that told him that his "Throttle Body was fine and does not need replacement. He went ahead and replaced just the wiring harness.

Hence the reason for my question? The only symptom that I have right now is a slightly elevated idle speed, i.e.: 750-80RPM, when cold and than subsided slightly to around 700-750RPM when the car warms-up.

Not sure if that helps

Phil

Diesel's don't have a "Throttle body", the IP controls the fuel and engine speed, I think.

I've never seen a 606 but the fellow that resealed my IP showed me a 606 that had electronic throttle control. There is no rod or cable between the pedal and the IP. Maybe the stepper motor or whatever controls the throttle on the IP is also called a throttle body.

Sixto
95 S420
87 300SDL

On a normally aspirated 606, there are two different flap-like devices in the intake tract; one of them they may be mistakenly called a throttle body due to its appearance & function.

It is the first one in the airstream, at the passenger side of the engine and attached to the large crossover tube that leads to the intake manifold. (The other flap valve is inside the intake manifold itself, and is used to tune the intake tract resonance for controlling the power at low vs. high RPM’s.)

The first one acts like a throttle body and apparently controls the amount of air as well as somehow regulating the amount of EGR being drawn into the engine as well. (yes, there is an EGR valve, but if this “throttle body” is closed, it will place a tremendous vacuum on the EGR port and increase the amount of EGR flow.) That all being said & done, it doesn’t make much sense that there would be any failure of that unit in conjunction with the wiring harness. It is controlled by an electrical connection/solenoid via a vacuum pod that actually does the physical movement of the valve.

Also, the NA 606 in my 124 does use a cable & linkage to the IP – it is not electronically controlled (except for the idle speed apparently). I think that the later ones (turbos only???) do use an electronic control for the IP.

Thanks for all of your replies.

I went to my Mercedes dealer today to inquire about lowering the idle speed from its current 750-800 RPM back to the normal 600-650 RPM. The head mechanic told me that there is no adjustment for that, that my problem is probably sensor related. He may be right about the high idle speed being possibly caused by a sensor or the wiring to it, but I believe that he is wrong in stating that there is no idle speed adjustment on this cars.

The information that I picked-up from "ALL DATA" for my car, and from other members on this, and other Forums specifically explains that there is an adjustment for idle speed. Basically its done by turning a bolt clockwise on the Fuel pump.

I trust the members of this group, more than I trust my Mercedes Dealership's mechanics.

Thanks again,

Phil

I'm not sure on the 606 but on my 603 their is a knob numberd 1-9 right behind the fuse box on the drivers side, turning it controls the idle. I'm sure their is a way to do it on the 606 the problem is you will have to pay the mechanic $100 just to look for it! :eek: