Hi all, before you guys jump on me for starting a new thread on the TPS, I have to say that I read all of the threads on the topic first before starting a new one. My problem appears to be a little bit different or maybe a more mature stage of the problem discussed in the other threads.

For the last few weeks I was experiencing that the car was difficult to stop esp in the first 15-20 minutes of driving. It would drive ok at any speed as long as i didnot have my foot on the brakes. The moment i would try to break ,it would become jerky and become difficult to hold just like when your dog is trying to run pulling you with it while you are holding onto the leash sort of thing. I would have to press the brakes super hard and the car would start to rev up say 500 more than usual and the problem would disappear after the first 10-15 mins of driving. I thought it was probably my transmission acting up and prolly my fluid level was not correct, because one thing that I did learn from Glynn is that these cars are extremely sensitive to the tranny fluid levels.

Anyhow, the real fun began this morning when i turned the car on, the car revved up to 1500 and then started oscillating around that number, it seemed at a very high frequency it would rev up to 1600 rpm and then the power would be cut off and it would drop down to 1400 and then power would kick in and then go up to 1600 again, all of this happening very fast multiple times a second byitself. Ofcourse the throttle was completely cut off so pressing the pedal had no effect. I also got the ESP message along with it. Next I proceeded to start the car in the Dyno mode to rule out of the ESP issue and the problem persisted. Then, i tried to reset the throttle using the 5 second procedure, it reset - i heard the click but the problem remained. The severe oscillation in rpm and the vehicle would only happen in the N and P positions, the moment i would shift to R or D the oscillations would stop the RPM would stabilize (higher than normal) and the car would be ready to jump soon as i let my foot go off the brake pedal, i let the car drive itself and it started to pick up speed until it hit the point of changing out of the first gear and at that point i could feel the transmission choking but the car remained in the first gear it is important to mention that accelerator remained completely inoperative, pressing it would not make the car pick up speed more than what it was doing on its own.

I stopped the car and got PO730 along with PO120.

I did make a small video to demonstrate the symptoms and here is the link.
The funny thing is half way into the video when I started the car again, the problem completely disappeared as if it had never existed. The accelerator was responsive and operational again and shifting was back to normal, however, the glory lasted only for as long as the camera was on!!!

2003 C230k M271
Mileage: 187,000 Km

 

Come on guys, over 200 views and no response.... you bet I am hitting the refresh button every minute :P

 

Hey Ammar_Rage, where are you in Toronto?

Naa,... I just think you're hitting refresh button every 5 minutes,... why? hockey season is over, Toronto Blue Jay sucks, Toronto soccer club sucks, Toronto football team haven't started yet,... so there's no real sport worth watching,... so hitting refresh every 5 minutes is as exciting as it gets in Toronto these days!

Why do you think its not the transmission,... did you check your transmission fluid level at 80C? And you made sure you don't have that leaking pilot bushing adaptor (transmission plug), right?

P0120 Throttle/Petal Position Sensor/Switch A Circuit Malfunction
P0730 Incorrect Gear Ratio

Anyways,.... when you idle it should idle around 700 RPM,... your car is idleing around 1500 RPM and not smooth,... I'm thinking too much carbon build up! At 187K km,... have you ever cleaned your fuel injector system, throttle body, MAF, etc.? The Mercedes-Benz recommended fluid is Chevron Techron for carbon build up at fuel injectors,.... but its a pain to find in Canada. My suggestion would be drop by your local CrappyTire,... err, I mean CanadianTire eh,... and grab some SeaFoam motor treatment,.... and the SeaFoam Spray as well. They're about $12-13 each.
http://www.canadiantire.ca/AST/brows....jsp?locale=en
http://www.canadiantire.ca/AST/brows....jsp?locale=en

Pour 1/3 of the SeaFoam motor treatment into your 1/4 tank of gas, 1/3 in your engine oil, and remaining 1/3 in vacuum tube. SeaFoam Spray 2 minute pass your MAF into throttle body,... Do NOT spray it on your MAF!

Oh,... I notice you film in a garage,... probably condo,... don't SeaFoam in there,... it'll smoke the place up big time! We're talking more white smoke than a Cheek&Chong movie,.... its best to aim your exhaust pipe at the house of someone you're not very fond of. If you don't have anyone,... then I can suggest a couple of my neighbours! There WILL be a lot of white smoke coming our of your exhaust pipe for a few minutes,... once it clears, take the car out for an aggressive drive on the highway.

Oh,... and take better care of the car,... you need new brake pads and left front bulb. For ESP, try resetting ESP by turning on the car, have it in PARK and turn steering wheel all the way to the right, then all the way to the left, repeat a few times,... 2-3 times should be good.

Report back after you SeaFoam the car,.... even better,.... post the SeaFoam smoke-out on YouTube!

 

If your identified the TB, ECU, gas pedal sensor are fine then it's your Engine Harness shorting somewhere. I had this problem with my C32 for9 mmonths and just before giving up I changed the engine harness and wow everything is perfect. Running like new.

Problem is even when plugged into the STAR it doesn't give a fault code for the harness, so usually no one changes it.

 

Since you are so sure it is not tranny, reconnect ECU and TCU and see if it changes. Dirty TB might be the cause as well, so clean it (see post above).
If none helps, with the car running go around and try pulling wires, you may get lucky and find loose wire or short. Other than that you need special equipment (e.g. STAR) to check different sensor readings and see what is out of normal.

Igor.

 

Thanks guys for your input, i agree with all of the above and have done most of what you guys have suggested, including cleaning the TB and the injectors etc. My only question is if it is any of what you guys have suspected then why would it render the gas pedal inoperative .. and throw po120???

 

I would question tranny code, not the pedal. ECU does not like one of the inputs or just acting up on you - I would say it is the pedal, if it was consistent.

 

good point budd, but the tranny code only popped up when i tried to drive it while it was pulsating with no throttle.

 

Aha, that explains it. Now that TB is clean (usually first suspect of jumping RPM) and you checked the wiring under the hood (second suspect), you need to test pedal output. BTW - if you have the equipment, I would reset/reprogram the idle just to eliminate simple ECU glitch. Just strange that problem is not consistent...

 

Thanks Accel, i will look into the wiring again. Because it is intermittent thats why i would prolly suspect the pedal more since it is characteristic of some flaky sensor problem.

@SunnyRay - I am right downtown budd and with all of our teams performing so well lately i was actually that bored and hitting the button every minute.. :P Where are you in Toronto.

 

If you want a long term fix, change the engine harness. Unstable current will throw all sorts of codes, today is Po120 I'm sure later you get a TB code then followed by ESP when the harness conditions deteriates. You sometimes can't see or measure the problem.

 

like john said change the engine harness. Had the same problem last year and worked like a charm.

 

thanks guys for the input. John and Cinder, could you guys elaborate on the problems that you were experiencing so I can see if i am noticing any other similar symptoms to narrow down the problem. How costly is it to do the engine harness, a rough estimate would be great. Cheers!

 

Seems those that have actually experienced this believe its your wiring harness that's the source of your problem.

A wiring harness from the Mercedes-Benz Stealership won't be cheap,... probably around $500,... plus another $500 for labour. You could probably find a used wiring harness at a salvage yard. It won't be easy to install, mainly a pain since its like a spider with wire arms going all over the engine.

If you're current wiring harness is shorting somewhere,... it's likely at the connector,... likely moisture or oil in the connector. My suggestion would be to salvage your own wiring harness,.... pull out each connector and clean any oil with CRC QD Electrical Cleaner and make sure they're dry before you reinstall.

Check that your cam magnets (two puck-shaped thingy near front top of M271 engine) aren't leaking oil. SEARCH,.... some with this issue have had to clean their wiring harness of oil,.... so theirs probably a DIY or online instructions somewhere,...

And I still think your car will benefit from a SeaFoam cleansing,....

I'm an uptown guy,.... Yonge-Sheppard-401 area.

 

Sorry for the late update guys, i was out of town for work for a few weeks. Ok, I brought the car to my mechanic and he thoroughly checked for vacuum leaks and found none. His diagnostics found the code 2201 or something which basically said "sensor voltage 2 below minimum ....." so he was pretty sure it was the TPS and ended up replacing the whole unit with the accelerator ($400 parts and labour). My wife got the car back while i was away and according to her it was working alright after that, anyhow this morning when i jumped into the car to go to work it started doing the same shi$$. I turned the car off...waited for a 10-15mins and turned it back on and everything was back to normal.

I did check the wiring harness for any signs of visible wear and tear but stuff looks good, nothing unusuall than the normal dirt..... any thoughts?? if its the wiring harness then you guys are suspecting a temp. ground somewhere...is that right? I mean it still gives me the same code (PO120) after having replaced the TPS i dunno what else could be the problem....any thoughts?

Thanks for your time and the input. Cheers!!

 

If you changed your TPS & TB, the chances are that there is nothing wrong with it. Its your Engine Harness playing you around, you will never get the code from the star.
You should of just changed the Harness instead of the TPS as the cost is about the same, it just easier for the mech to change the TPS.
I might be wrong but after 9months of fussing around and changing everything and spending lots of money and a brain dead mechanic, i finally got another mechanic and told him to change the harness.
Most garages dont use there brain too much, they rely on the computer to tell them whats wrong.

Dont take my word, just think about it..

 

Thanks John, I wanna ask you a couple of questions budd... so what were your symptoms, were you experiencing the same symptoms as mine where your throttle is completely cutoff and rpm goes up and down quickly kinda seems like engine is gasping..

Secondly, how much did it cost you exactly to get the harness replaced, if you could provide a breakdown of part and labour that would be great!

 

Symptoms are the same as yours, sometimes it wont start after stalling. The rpm would hunt from 1.5k to 4k, also after pressing the gas the rpm wont drop back down.

The harness cost ~$600 for my car, i wouldn't expect it to be any higher for yours. Labour cost is about $150 to 200. It should be easier for your car.

 

AR - sorry so late. So you have a new TPS. Please don't put Seafoam in your oil & use Techron for fuel.

The TPS Hall sensor is two channel so I doubt a new one would be faulty. Check for vacuum leaks in all pipework & check that you don't have a ruptured diaphragm in your brake booster or a sticky valve. It worries me that braking effects this.

Your implausible transmission code has nothing to do with this engine behaviour & is likely spurious.

Do you have oil in your harness? Check the upstream O2 sensor plug. That's where it usually shows first.

Good luck!

 

Thanks Glynn, i was wondering why i had not had ur input on this..lol There are no vacuum leaks as much as I cud check and there is no oil in the harness again as much as i cud check. I cant think of anything else, its been running fine for the last 3-4 days. I do 150km on it every day for work.

 

I'll bet you have a valve in the brake booster that sticks now & again.

If it happens again. stomp on & off the brakes many times & see if it relieves it.

 

Thanks Glyn, I will do that, is there any other way to check for that? By the way this is the code that the mech. got using his diagnostic system before he replaced the TPS. "Throttle valve potentiometer voltage 2 is too low.""

Its pretty clear from the code that its the TPS however I find it hard to believe that the new TPS is also bad, something is triggering this code.....

 

Vacuum leaks can be a pain. They don't thow codes generally unless chronic which can give you a "fuel trim lean" message.

Let me explain in simple terms how a vacuum leak can cause what you experience. It lets more air into the engine without the throttle plate being opened & initially the MAF will respond & revs will rise. Then the ECU detects no throttle input & says wait a minute ~ no throttle input & throttles back the MAF to lean & the revs drop. This is to prevent a runaway engine.

I have little doubt that the TPS hall sensor was playing up. Remember it is two channel & the chances of both conductors in the harness being faulty is slim unless there is oil in the harness then all bets are off because it can corrupt everything across multiple conductors.

 

Giving your issue some more thought it might not be the brake booster if your car has a vacuum pump that is deleted on newer models. If your engine is fitted with a vacuum pump then I don't understand how the brakes can effect the problem you explain.

Could be another vacuum leak & remote possibility that it's the EGR system.

 

I had the same issue with my 02 c32 120k mi. it turned out to be a dirty tb, quick shot of carb cleaner fixed it. What glyn said, techron only, at regular intervals for higher mileage vehicles.