Throttle Actuator

[bimmerman]

I have a 93 400E and am in the process of changing the harness. I see mention of a "throttle actuator" on many posts on this site. Can anyone tell me what it is, where it is, and why it is? I am used to Bimmers which do not have such things (but seem to be over engineered just like the Benz machines). The only thing that keeps me from trying a big Lexus is that they are just too "mundane" for me. Plain vanilla! Thanks.

Garry
93 400E
92 735
88 635

[y2kimmel]

I believe that the throttle actuator is amidships, right against the firewall, behind the engine (if you're looking from the front of the bay).

The actuator is connected to the accelerator cable, which is connected to the gas pedal. I know - this seems silly to have a cable when there's a $1000 actuator to operate the throttle.

The Throttle actuator, as far as i can tell, is there to allow for the operation of the Acceleration Slip Regulation (ASR) feature. When the system senses wheel slip, it signals the throttle actuator to back off on engine throttle to eliminate slippage.

My car doesn't have ASR, but it still has a thorttle actuator. Probably easier for MB to throw this part in than to design a separate cable-controlled throttle.

By the way - BMW does have the same sort of thing for their version of ASR. It's called EML (Electronic Motor Load, i believe). it first appeared on the 750, and later on the V8s in the 540 and 740. Could have been on the 735/535 in the last couple of years of production as well.

Hope this helps. Pray that your throttle actuator is healthy. It's $1000 for the part. A not-uncommon failure item on these cars.

Troy
1995 E420 77k

[bimmerman]

Thanks Troy. As soon as I get the harness installed I am putting this car on the street with a for sale sign in the window. It is a neat machine but all the posts I read are scaring me. It seems like the older versions (mid eighties) of these German cars were much simpler, easier to work on and way less problems. The only repetitive problems I have experienced with my older BMW's (88 through 92) are things like drive shafts and heater cores. Simple, straight forward problems. I would never own a newer V8 BMW for the same reasons. I am retired M.E. who believes in simplicity.
Thanks again for your input.

Garry
93 400E
92 735
88 635

[eandytemp]

I have two of them if anybody needs one.

Andy

[shane83SD]

Hi Bimmerman,

I'm with you on the new generations of MB and BMWs. I had/have 73 2002, 78 530i, 90 525i, and 91 735i. I would not touch those V8 and V12s. Wife got a 98 C280 since new, drive by wire, etc etc covered up by engine cover, pretty much un-serviceable by mere mortals.

Last November, I bought a 83 300SD. It is now my daily driver after I got it up to snuff. Thanks for this wonder forum, it hav'nt seen any dealer or indy shop. With a turbo to play with, it is a lot of fun.

[deanyel]

The throttle actuator, or engine actuator, or throttle body sits on the intake manifold, or on a V8 in the middle of the engine. It's primary function is to regulate the air/fuel mixture. They are made by both Bosch and Siemens VDO. Follow the air flow through the air filter and you will find the throttle actuator. They usually cost about $1000 but they don't fail nearly as often as they get replaced. A good cleaning will often solve the problem. I think you have one of the great cars there, and while the engine bay is tight for a DIYer, you're not likely to find anything before or since that is as durable and long lived.

[bimmerman]

Thanks for the suggestion. Can you tell me what I need to remove to get at the throttle actuator, and how to determine if it is bad? As I do not have a shop manual or CD for this car I do not quite understand where it is or how it works (and why it is even needed). Is it a device that electrically operates the throttle plate in the body (as opposed to a simple direct linkage)? Is there a web site where one can get a theory of operation of this system with schematics, etc? I am capable of doing in-depth work on the many Bimmers I have owned over the years but this particular problem is totally new for me. I really can't afford $80.00/hour at the small town dealer we have here, plus I do not have immense confidence in them. I really appreciate everyone's help. This is a great board!

Garry

[deanyel]

Take off the air filter housing and you should be able to look down and see the butterfly valve. It's sort of an electro mechanical device controlled by the engine management system based on inputs from various sensors and systems in the car. You might get some insight at siemensVDO.com. They refer to them as engine actuators. As I recall you can download a product catalog that has at least some basic information on how they work. Cleaning the whole thing up is the easiest, cheapest thing you can do. There is a place on their web site that says that replacement parts are available to rebuild them but I looked high and low and could not find them in the U.S. I think MB USA likes selling the replacement units.

[Kebowers]

whose web site mentioned repair parts? I'd like to know so I can also search for them.

The common failure is the wire insulation inside the wiring bundle attached to/integral with the throttle actuator.

The throttle cable merely moves a variable resistor which tells the engine control system to 'give me more power'. The actual throttle opensing in then determined by the engine management system--which tells the motor that drives the throttle plate, to open up. The actuator also contains a position sensor variable resistor that allows the engine management computer to determine the throttle blade position and verify that it is where it is supposed to be. If that senros position does not match what it is supposed to be it goes into 'limp' mode.

[Gilly]

On a M119, it's actually under the mass airflow sensor. It's hard to get at the clamp to remove the sensor and the rubber "collector sleeve" under the sensor. The actuator itself is in a location sometimes referred to as "the hell hole". If you're not experiencing any throttle problems (variations in engine speed, poor or low idle, engine dieing, etc) I'd just leave it alone.

Gilly

[bimmerman]

Thanks Gilly and Ken. I can think of only one word that can possibly describe the needlessly complex, ordained to be problematic system you have explained to me here: Kluge! It takes me back to the Paris Air Show where the great European A-300 Airbus was making it's initial "fly by wire" debut. The pilot had one hand on the yoke and the other on the throttles as the plane lifted off the runway, then settled back down into the trees, bursting into flames. It seems the pilot wanted to take off but the computer wanted to land. The computer won. The throttles were useless in the pilots hand as the electronics were driving them. Perhaps a poor analogy, but some similarity none the less. I borrowed a MB W-124 service CD today so now I have some understanding as to how this Rube-Goldberg thing works.

Garry

[Gilly]

I don't think you're supposed to hyphenate Rube Goldberg. It's what most MB technology is based on, so show a little respect. You should capitalize "Diesel" too!

Gilly

[bimmerman]

Very Good. I stand corrected!