Many of us have been plagued with intermittant ASR problems.

In most cases, diagnostic codes point to the engine throttle body, which unfortunately is about $900 retail.

A member was kind enough to drop off his "bad" throttle-body.
Although it had "security" TORX screws, I was able to get the proper security bit, and open up the throttle body.

First impressions: this baby is complex! Not only does it have a circuit board, small motor, gears, springs and a fancy potentiometer, everything is IMHO overly COMPLEX. No wonder it costs over $500. That's probably just the material and labor costs. Figure in some profit, and BANG $900-$1000 from the dealer.

Closer inspection showed some major problems with the wire's insulation. They were cracked and shorting out among themselves and the body. Looks similar to the dreaded engine wiring harness insulation disintegration!

Also, the solder-pads were full of flux, either from the heat of the engine, or a poor solder job.

IMHO, MB did a POOR materials engineering on this product, and unfortunately, we're paying for it.

Gives new meaning to, "engineered like no other car in the world"

I'll try and "fix" the broken insulation and see if it fixes an intermittant ASR problem in the next 2-3 months.

:-( neil
1988 360TE AMG
1993 500E
==========

Very nice pictures.

I guess all of the wiring they used from '92 through early '95 is suspect on all the different components.

The throttle actuators on '93-'97 M104's also go out, and they cost $961 here at ParsShop, and the reason for the failure is usually the wiring harness.

That's right, it gives new meaning to the phrase, "engineered like no other car in the world..."

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

Great pix, Neil. So, at this point, does it look like mechanical failure of the insulation and possibly heat damaged solder joints only? Any apparent component failure?

__________________
Glen Tokuhara
Beauty & the Beast and the wagon that could!

Yyyy...uuucckkkkkkk...

What the $%^ were they smoking when they approved this wiring? I have opened up 50 year old radio's with wiring in better shape than that shown in the pictures, even with the heat.

Looks like a 1-2 hour rewire job (max) on the bench to R&R the wiring and resoldier the joints. This stuff is not that hard to replace, it's just getting the new pot that seems difficult.

Removing the TB's wiring harness will be a ROYAL PITA, and I am certain they are also disintegrated, esp. since they don't have a metal body to protect them from heat!

I haven't measured any of the other components, so I don't know if they are fried.

I am more than willing to send this out to someone with more experience in electronic troubleshooting.

:-) neil

Neil,

You've got mail...

Hey...are the new-out-of-the-box throttle bodies better than the stuff originally manufactured or was this poor design perpetuated?

__________________
Jim

1992 500E
2007 CLK63
2003 Audi RS6
2001 Audi allroad

I have heard from reliable sources at MB that the problem is with the microswitch. Bosch will not rebuild or make available the part.

I had to replace mine. The part was $485 from my dealer.

A couple of thoughts:

The boiled-off flux ought to clean up relatively easily.

There are insulating epoxy resins designed to be painted on to cracked insulation; if it's possible to see and access all of the wiring with the unit open on the bench, it ought to be possible to shortproof them.

The microswitch/potentiometer (are we talking about the same thing, or two different items?) might be the real sticking point.

It's been fairly rare in my experience for a component manufacturer to do fully specific bespoke designs for anything other than maybe black-world, cost-is-no-object military aerospace stuff. Nonrecurring tooling cost kills componentmakers' margins on small production runs, so they try to avoid those.

There may be a chance that Bosch builds and sells a more or less identical component to other manufacturers -- perhaps not even auto manufacturers, but somebody. It might require access to an internal Bosch catalog not normally released to customers in order to crossreference the numbers.

This reluctance to let anyone but a licensed MB rebuilder have access to the part may also be driven by MB legal. I would bet that anything having to do with throttling fuel delivery is a big red flag for corporate liability exposure.

Anyone remember how Audi was nearly killed by "unintended acceleration" claims and lawsuits? And they didn't even do anything wrong; their vehicles turned out not to have any technical faults.

s/b

One more sodden thought:

Can the electronics be separated from the case? It might be helpful to have it sent out for an insulating ceramic coat to keep the heat down.

s/b

Wouldn't it be cheaper/faster/easier simply to epoxy-coat (JB Quik) the entire PCB (a-la-software-copy-block-keys)?

That would address all heat/cracking/melting issues...

Reviving this old thread with new information:

I just pulled the TBA from my own 500E for inspection.

Instructions on how to do it, plus a lot of pissing and moaning about the lack of detail of previous comments, can be found here:

http://www.peachparts.com/shopforum/mercedes-benz-performance-paddock/68942-500e-throttle-actuator-removal-post431308.html#post431308

Now that I have the TBA off the car, I have opened the case on both sides and inspected. This unit is apparently factory original, a '93 production run on a '93 vehicle.

It has none of the faults shown in Neil's excellent forensic photos. No resin runs, no solder cracks, no wire insulation breakdown.

I slit the jacket open of the data cable that runs from the TBA to the computer. No wire deterioration there, either.

This car *did* have a failing deteriorated injection control harness, so I know what to look for. But no, it's OK. The car has zero history of overheating, so that may have helped the wires stay in good shape.

I think I'm just going to rigorously seal up the unit after treating the electricals with DeOxIt (an electrical contact enhancer) and get it back in the car and have a long drive.

The one thing I wonder about is whether I should lubricate any of the rotating mechanicals.

s/b

Following up:

I continue to find everything in good shape on this TBA. The one thing that jumped out at me was that the underside of the throttle plate was absolutely caked with black combustion tar.

I cleaned all that off, and it was quite a job. Bottom layer on the metal was tough varnish that laughed at solvents, and had to be gently scraped with a pick.

It appeared to me that if the crud on the plate bottom had gotten much thicker, it would have begun to interfere with the free play of the plate on its center shaft. Could this be a reason for TBAs dying? If the motor has to work beyond spec to move the plate, it'll draw excessive current, and heat up the inside of the TBA assembly. Hmmmmm.

Another reason to get the crud off: turbulent airflow. I doubt I'll feel much difference at the throttle from just that, but we will see.

Speaking of the throttle, I am amazed that this five-liter engine is able to breathe efficiently through a throat this size. I've seen bigger throttle bodies on four-cylinder rice motors! The mod suggests itself of having the center overbored by another few mm, and machining a newer larger plate to fit.

Right now I am going through and renewing the internals. Gaskets are being removed gently and checked. They look OK so far, but they are visibly drying out. I am treating them with Rubber Renue to restore their original bouncy plasticity.

Electrical contacts both inside and out are being lubed with CAIG electrical contact enhancer. I have applied some light persisting penetrating oil to the plate shaft.

The motor works through a plastic gear, of which genre I am not fond. I suppose it could be worse -- this could be a GM car with plastic cam sprockets! But the gear itself shows no real signs of wear. I might put a tiny layer of synthetic grease on it just to be on the safe side.

s/b

So did it work ?

:-) neil

...to do the coolant sensor resistor mod. I think it's clear that high under hood temps. are doing more harm than we know.