Our 1997 E300D just set OBD-II code P0120. Generically speaking, this is a throttle position sensor code. I guess that I didn't realize that this is a "fly by wire car". There had been some complaints of "surging". Oddly enough, the surging quit after the code was set. Can one of you Master Technicians please lend me some advice? Is this something I could fix or replace? Or is this generic code misleading? I like this car, and want to keep it. It's delivering 31 mpg in mostly city driving.

Thanks in advance for any and all help.

I have a 96 with the same engine. It too surges from time to time at certian throttle poisitions.

There is a throttle position indicator that is located roughly in the area of the brake master cylinder. If you use a scope to look at this signal, I would think you might find a bad spot in one of the positions.

I'm sure Benzmac would concur that the most common reason for 606 engine surging is caused by sticking resonance flaps. I an unsure what or even if codes are set by the flaps sticking. There are 2 of them, one in the middle of the air tube on top of the engine, the other is under the intake manifold near where the air tube attaches. I did fix one 210 chassis Diesel recently, very high miler, which was fixed by adjusting the pump timing.
Gilly

Faulty electronic throttles and wiring harnesses
 

Every one of the Benz gasoline engines with the electronic accelerator/cruise/idle systems (the throttle by wire)has failing wiring insulation. Apparently Bosch got a bunch of low grade PVC wire and the stuff crumbles after a few years. I have looked at several recently after finding it in both actuators on My sl-600. An independent shop here in Houston had a basket full of 'cores' they had removed and were stocking--waiting for someone to start repairing them. The wiring is not available from Bosch or Benz. After getting a 'pin-out' wiring diagram it took me a couple of hours to make each new one.

Lot and lots of these things are failing (surging, throttle position errors, dead, etc.) and 'the fix' right now is replace them. Crappy wiring is the flaw.

So the main wiring harnesses on 140 and 129 cars are all crumbling, all the electronic throttle actuators are failing--sounds like a class action suit waiting to happen. When a $140,000 car has multiple wiring harnesses that fall apart in less than 7 years, something is badly wrong. These things are real safety hazards.

Has anyone heard of a class action yet?

Any new info on this one?

My father's 96 E300D (w210 non turbo 606) has a CEL that comes on for the throttle position sensor. I replaced the unit up there by the brake booster (throttle wire, a linkage and an electric circuit all attach to this $355 part), but then the light came back.

Originally it seemed to be caused by using the cruise, but now its come back without cruise usage. I have to guess that its something to do with the wiring, as I can't imagine the MB part was bad (maybe not the old part either).

I really need to get this TPS code to stop coming on, so thaqt I can get the car inspected (code=automatic fail, and I cant get it from home to the station without a code coming on).

We have no surging, but maybe the resonance flaps are sticking (I took the intake off and there was a LOT of gunk in the ports, and since Ive cleaned it all out, probably loosening some of it, now the egr valve sets a code, which it never did before, telling me that is probably a bit clogged). Would a sticking resonance flap cause a CEL for the TPS?

Oram I looking at a pump problem that will require a pump adjustment or replacement?

Any help would be most appreciated. The car really needs to be inspected, I cant and Im at my wit's end for fixing this thing.

Thanks,

JMH

Hi SteveB

Underneath the air cleaner assembly are two vacuum transducers, one of them may be the source of your P0120 code. It may also be part of your surging problem. If the surge is still prevelant then you may want to consider new resonance flaps as they do get coked over time.

I would imagine you have already replaced all the plastic fuel lines at the pump and filter assemblies? I have repaired several intermittent surge conditions by replacing all the fuel lines in the engine compartment.
:)

MrCjames and Gentlemen,

Wow, thanks for the replies. I posted that one a long time ago.

You guys are right, the problem is related to the resonance flaps.
It seems that Mercedes, in their infinite wisdom, decided to plumb both the crankcase vapors and the EGR gases into the intake manifold. Let's see, oily vapors mixed with hot exhaust gases......what might that cause? Carbon? Or the "gunk" that you have described in your intake manifold? Probably.

Mercedes' solution is to remove and hot tank the intake, and clean or replace the resonance flaps - over and over, again and again. If this weren't problem enough, this has to occur quite often. My car isn't weak or sick. It doesn't use or leak oil, and does still achieve very high fuel mileage. But this regularly occuring service practice is unacceptable.

I complained as far up as I could find someone willing to listen, but the reply was usually the same B.S. "You are the only one that seems to be having this problem, and no, we don't have a way to solve it." Yeah, I'll bet I'm the only one having this problem.....sure. And you could solve it, but you won't.

I thought about complaining to the EPA against Mercedes, planning on employing the idea that their emission control system is neither robust nor reliable enough to function for a reasonable lifespan, but this move would not fix my car so that it would not have it's own parking space at the local dealership so I abandoned this idea.

My car (and it's problem) is now fixed and has not been back to the dealership for this problem in quite a while.

How do you fix this, you ask? Well, one thought might be that between the hot exhaust gases and the oily crankcase vapors, one (or both) of them has to go. Of course, I cannot recommend modifying or changing your emission system. And no shop would touch a modification like the one I just described. So, get your thinking caps on and get creative.

I guess the aggravating part is that Mercedes just seemed to "shrug their shoulders" and give me the "that's the way it is" type of answer. Building a car with a recurring service problem is stupid. It's also stupid of Mercedes to think that people who have experienced what I have will continue to buy their product based on brand recognition, reputation, or the "status symbol" that many think the car affords them. I bought this car after owning an earlier model that was "dead on" reliable. You can see in my signature that "status" is not my thing. My cars are older and used, usually. I just need them to be dependable, comfortable, and efficient. My next luxury sedan might have to be a Lexus or Infinity. I'm sure that they can solve any problem that might happen (heavy on the MIGHT HAPPEN) with one of their cars.

Well, thanks again for the reply and advice. I love this website.
I'm going to jump down off of my soapbox now.

Steven

So let me get this straight... the problem with your throttle position sensor was actually due to the resonance flaps?

No wonder I couldnt get the light to go away by changing electronics.

Thanks,

JMH

JHZR2,

No sir. I don't believe that the TPS was the problem at all.

As I understand it, the resonance flaps "adjust" the theoretical "length" of the intake manifold, according to what the operating conditions are, i.e. rpm, gear, load, throttle position, etc. Someone jump in here, if I have it wrong.

Think of the old days when the Max-Wedge Plymouths ran a manifold design called the "cross-ram". This was a high rpm item only. It performed poorly at low engine speeds. With the resonance flaps, Mercedes can make the engine perform better at all engine speeds and loads - it "shortens" the intake for low-speed events and "lengthens" the intake for higher engine speed operation (depending on a lot of other information sent to the engine's control module by a bunch of sensors). The path of the air thru the intake is "tuned" for the best cylinder fill by opening or closing one, or the other, or both of the flaps. I guess that Mercedes was trying what they could since the 1997 models weren't turbocharged. Again, if I have this wrong, someone correct me, or help me out. Even if I have it all wrong, my assumptions helped fix the car.

I think what was happening to me was that the gunked up intake was causing the flaps to stick (and sometimes break), setting a code. The odd thing is that the drivability didn't suffer that much; the check engine light was annoying. The dealership never replaced the TPS, and neither have I. I don't doubt that they can be the cause of problems like this one, I just don't think it caused mine. Also, let me clarify something from my original post. Surging in my car was almost unperceptable, if not non-existant.
I think my comments were related to others who have had surging problems.

Again....no carbon or "gunk"......no stuck flaps......no problem.

Good power (for a naturally apirated car) and great mileage.

While we are here, does anyone know how to shut down the "anti-spin" feature or traction control.... I can't remember what Mercedes actually calls it. Sometimes we don't need for this to be working.

Steven

Great info, thanks!

JMH

Great info
 

I thinkI may be suffering the same but in my case I'm also getting a "hard shift" unless I gun it and this just eases the hard shift - doesn't cure it. I've never cleaned the flaps and I'm currently at 264K miles (owner for the past 180K miles) so i know I'm due.

I do have:
- hard shifting issue
- leaking fuel lines (replacing tomorrow)
- gunked up manifold (getting cleaned tomorrow)
- CEL with an associated EGR code (due to the above I'm told)

Will the cleansing of my manifold rectify my shift issues? i don't see any obvious breaches in my vacuum lines - up front or near the TPS.

Thanks for any other suggestions.