Adrenojunky

Hello all - new here... I'll get straight to it - my wifes got a 2002 C230 Kompressor (2-Door) w/about 60000mi. We've never had any real mechanical problems with the car since she's had it - just a wonky suroof and wierd HVAC operation... All maintenance is up-to-date, and I do all that. So - we were driving back to Phoenix from SanDiego on Sunday afternoon - about an hour out of Phoenix, I had the car on Cruise Control @ 85mph (as it had been for the previous 4 hours), and bam - engine starts sputtering out and dies on me - felt just like running out of gas (had over 1/2 tank). So, immediately I assume we might be having an overheating problem (since it was 117 degrees where we were) - and switch the computer display thingy over to show engine temp, which was fine (less than 100 deg C). Popped the hood - had a look around, nothing out of place. No smells (oil, gas, tranny fluid or engine coolant). So, I get back in, and start it up - starts just fine, and off we go... Got back up to speed and made it about another 20 miles and it does the same thing. This time I noticed though that the engine didnt shut off completely, just reduced to idle. I put it in neutral and tried revving the gas, but the tach stayed right at idle - like it wasnt recieving any throttle at all. Very strange... I pulled into a gas station and let it cool off - and checked all fluids and had another look around - nothing. Everything seems fine. So we headed off and it turned off on us 3 or 4 more times until we got home. Seemed as if I needed to turn it off, stop, wait a minute and then it would just start right up (and run rough for a couple seconds - then right itself) and motor on just fine until it decided to shut off again... Very strange indeed...

So, anyone run into this before? I was hoping this was fairly common - but doesnt seem to be so...

It should be noted that the computer is not displaying anything - no check engine light, or any lights for that matter. So, given this, is there any sense in hooking up a scanner, if there are no trouble lights? For many cars (my Honda and Jeep at-least) the computer will display a CEL if the computer has any codes stored. And, if it is worth my time, can I get it scanned at the local parts store (Checker, Autozone, etc) or must it be done by an MB dealer? I'm not really familiar with MB's.

Here is what I think it could be, but I dont know these cars too well:

1) Vapor-lock (it was 117 out) - crappy gas...

2) Clogged fuel filter (would explain why it would only go ~20 miles every time, then have to be shut off, let the fuel pump fill it up, then off again for another 20mi).

3) Bad throttle sensor (assuming these are fly-by-wire type throttle?).

4) O2 sensors were 'overheated' sending ECU bad data, maybe making the car dump into a 'limp' mode of some sort - until they cooled?


Those are just guesses - I'd really like to avoid taking this thing to a dealership - I never pay people to work on my cars (was a mechanic myself for 7 years some time ago..). However, my wife is now driving my Jeep for her daily commute, as she doesnt trust the car - and my lifted XJ gets about 12mpg - so will cost us a fortune if I cant get it fixed soon!

Any help is greatly appreciated!

BTW - Can I pull the codes (if any) myself - wont display on the instrument display thingy?

Gullwing

Check codes.

Check the amp draw for the fuel pumps, if around (I think) 15 amps at idle that coudl be the issue. New pumps run around 10 amps at idle.

CPS probably wont all the car to restart right away, but if it has not been replaced yet... If you do replace that, also replace the connector.

Adrenojunky

OK - well the wife took the car to the MB dealer yesterday to have them diagnose the problem, because she swore that her warranty would cover it - warranty expired in May... Anyhow - they said it is a faulty Throttle Position Sensor (Thought it could be...) - that it is giving intermittent and eratic output.

So, new questions:

1) Where is the TPS on these cars? Is it in/on the throttle body as most vehicles - or is it somewhere else (since these are drive-by-wire vehicles)?

2) I cant seem to find these anywhere on-line. Does MB call this something other than a Throttle Position Sensor? Or do they use some other vocabulary?

3) Where can I find one, and how much do they tend to cost?


Thanks.

MBTHEONE

The MB term would be Accelerator pedal sensor.

Adrenojunky

"The MB term would be Accelerator pedal sensor. The problem I have with this though is that you said the problem happened when you had the car in cruise control. If that were the case then your foot wasn't on the gas and the pedal value sensor would read the same value the whole time. To me it sounds more like an issue with the Crankshaft Position sensor(Common Issue), but like Gullwing said, those usually don't allow you to restart the car right away.

GL"

MBTHEONE - Sorry - I got this in my email as your response - I was thinking sorta the same thing, but why did you edit? Is this not the case? I wonder if the cruise control's throttle control is directed through the Accelerator Pedal Sensor? How does this work with drive-by-wire type systems? It would be necessary for the ECU to send the actuator TP signals one way or another - or am I missing something here?

Thanks

MBTHEONE

I edited becuase I re-read the description of the problem you were having. When you said the vehicle would restart but when you would apply the gas pedal there was no RPM increase, which I've noticed on multiple cars with Accel. Pedal Sensor issues.

Cruise control gathers information from multiple control modules. It will usually retreive your speed from the ESP module and other various engine inputes from the ME, and does what it needs to maintain speed.

Adrenojunky

I do agree though - I cant see why it would stumble with the CC on due to the APS - unless it uses data from this to determine actual throttle position info.... Which would be counterproductive - I'd think it would prefer to determine Throttle Position from the Throttle Body (Butterfly) Valve. Is there another way in which actual throttle position could be acquired?

MBTHEONE

The butterfly valve you are thinking of has it's own seperate motor and dual potentiometers for measuring it's position. Much different than a normal car. Very seldom do those go bad, and when they do, there should be corresponding faults. Also, to answer your question, throttle demand is only acquired via the APS and the ME regulates the butterfly valve based on demand. Also when I've replaced the APS's there is usaully a corresponding fualt for the APS which will illuminate the CEL. If you still have the receipt of your paperwork from the dealer I would check to see if a short test or quick test was performed to verify that there were no faults in the system.

Adrenojunky

I'll check the paperwork as soon as I get it - car hasnt been picked up yet - I'll pay them for the diagnosis and fix it myself...

Next question is - where can I find one of these and what is the approximate cost? I've not been able to find any at all online... I'm sure it'll cost a pretty penny though (one of the reasons I stick to my Jeeps and Fords..). Or, if it's too bad, I'll head to the boneyard and pick one...


Thanks for the help.

Gullwing

If it is the throttle body, then I don't think you should replace it yourself.
Once it is replaced the engine probably wont run, it needs to be readapted before it will run correctly/at all.

MBTHEONE

Well I just did a quick search around google by typing "mercedes benz oem parts" and checked several vendors. None of them seemed to have the APS available. A junk yard would be a good idea too. If the APS doesn't solve your problem, the crank position sensor can be bought online it looks like, for possibly cheaper than the dealer.

And no problem with the help. I do this at work no when I have downtime to keep the lil gears in my head working

MBTHEONE

Yea, I wasn't trying to lead him to the throttle body as I don't think that's the issue. I was just explaining to him the "butterfly valve" he asked about.

Adrenojunky

Re-adapted? Whats this...?

Gullwing

If you touch anything on the engine (spark plugs, air filter, MAF...) the engine should be readapted. This resets the mixture adaptation and throttle position to factory settings, the engine then adjusts itself from there.

Adrenojunky

How do I go about this - for future reference?

Gullwing

Only way I know of is with a SDS, you can't just disconnect the battery to reset them.
Even with the SDS it can be a pain and require several attempts.