Hello forum,

I have searched this forum all over and I keep seeing MAF sensors and CPS sensors and TPS sensors and wiring harnesses failing and on the rare occasion a computer (ECU/EGM/TCU/?) failure. I'm trying to figure out why this 1997 C230 4 door Sedan with 160,000 miles will start then immediately "hunt" for a good idle spot. The rpm's just bounce up and down from 1000 to 1500 rpm's. I can let the car warm up to midrange temperature then turn off the ignition, start it and the rpm's will hold steady until I touch the gas pedal... just the slightest touch will set it off and then it's "hunting" for an idle. There is absolutely no other gas pedal response. If I floor it while it's running I might as well have just dropped the vanity mirror to style my hair. If I put it in Drive or Reverse the rpm's drop to about 800 and will either hold steady or bounce and lurch. If the rpm's are steady and I hit the gas pedal it instantly starts hunting and no longer cares about the gas pedal.

I purchased this car on the cheap because a Independent Mercedes mechanic told the Previous Owner that the car needed a computer and the EGS was bad. So I thought I'd challenge that theory.

That mechanic installed a Crank shaft position sensor (it had swollen up and had to be pressed out). They put a re-manufactured Throttle Body Actuator on, then an OEM Throttle Body Actuator with no change in the symptoms. Two years ago (and probably 30,000 miles) a different mechanic replaced both ignition coils were along with plugs and a couple of wires. One Injector was replaced also. (I have the receipts from the Previous Owner). They also replaced the Throttle Position Sensor a couple of years ago.

Since I've had the car I have installed a brand new battery, swapped out an ebay computer with the exact same part number: A 023 545 2332 . It will not let the car turn over. When I plug an ODBII scanner in it passes with 0 codes.
I put the original computer back in, and the car turns over and starts and hunts at idle like usual. Swapped computer and same results - Key turn, audible click and a weak attempt to engage the starter then nothing 0 codes. Original computer is now installed. So now I get the ODBII scanner plugged in and see Cam Shaft sensor out of range P0341 after it's warmed up to temp. I replace the sensor and since then I've cycled the engine up to temp about 5 times and the Check Engine Light consistently stays off. Then I checked the air filter. It was installed incorrectly with a one inch air gap where the foam edge was revealing a nice passage for unfiltered air to pass into the intake. Great. New filter installed and start it up and same results. I unplug the MAF sensor while it was hot and the engine still hunts but at a slightly lower RPM but I cannot verify that experiment completely. The absence of the MAF causes the two codes associated with it P0110 and P0100. If I try to clear the codes with the MAF unplugged they stay active. I plug in the MAF and clear the codes successfully. I unplug the Throttle Position Sensor expecting the computer to pass a code but there is no check engine light or code when I unplug the TPS, even when running. Someone suggests check fuel filter so we pull that off and it looks original. The filter is extremely clogged, you cannot blow hardly any air through it by mouth. Installed a similar size cheap $10 fuel filter while waiting for the correct one. Same results, engine starts and hunts. Put in gear and lurches with the hunting rpm's. If it makes it to over 10mp/h it makes a thunk noise and and cuts out for a moment then picks up. Its pretty crippled.

When idling the car is not blowing any blue/white/black smoke. It smells just like noxious carbon dioxide. The engine mechanically sounds pretty quiet.

While changing the camshaft position sensor the clear and brown vacumn lines crumbled in my hands. I replaced the broken/missing areas with black rubber vacumn tubing.

I'm wondering if:

a) I need to change the MAF sensor, it did receive unfiltered air for a period of time. There is traces of dirt and sand in the intake piping between the filter and throttle body plate. But no check engine light/code when plugged in.... ?
b) The absence of the TPS sensor should trip a code... right?
c) Does the TPS sensor need to be replaced? Maybe the wiring harness is providing enough of a short to tell the computer it's got the voltage it needs.
d) Why did the computer off ebay pass ODBII scan but will not let the engine turn over? Does it require to be reprogrammed? Can I desolder the firmware chip from one circuit board and solder it to the other?
e) Why am I not receiving misfire codes, rich/lean codes, etc. when it's running and bouncing the rpms all over the place.
f) Is it in some kind of limp mode that requires a fancier computer to clear?
g) Why did the mechanic start with the crankshaft position sensor, throttle body actuator, when the fuel filter was completely clogged and the air filter had a large section caved in causing unfiltered air to be sucked in? Why didn't I?
h) Is there a calibration necessary when replacing the battery or any components on a 1997 W202 C230?
i) Why the milage odometer will not illuminate. I can barely make out the numbers in the right light.

As soon as it warms up a couple of degrees outside I'm going to:

a) Unplug the wiring harness at the computer, unplug the TPS 5-6 pin connector and see if I can get any resistance between the wires by ohming them out.

b) Purchase some CRC cleaner and spray down the MAF sensor.


As of right now it's got no check engine light illuminated and no trouble codes

Thanks for reading if you've got this far. Sorry for the long thread I hope I've included as much useful information as possible. I hope someone can help me bring this car back into driveable condition.

 

Hi.

Have you got a solution to your symptom ??

I am having the same issue as you!! Mine is a C200

 

Sorry, no solution. Maf sensor brand new from autohauz ready to sell...

 

Hello, i am in a Garage that specialises in European cars, alltho i am not VERY comfortable with MB i have the proper tools to scan them.

I'm having the EXACT same issues with a 1998 C230.
I plugued in the diagnostic scanner (Lauch X-431) and went directly to the throttle valve to see if the tps was working, actuated the throttle by hand to see if the values change, nothing happen. I went in the actuations, tryed to actuate the throttle valve. Same thing, nothing happens. Called a used throttle valve, installed it, nothing works.

I checked the values for all other sensors, the MAF gives me a good reading at idle. All the other sensors work properly.
The only thing i am getting wrong is the fact i don't get any readings on the throttle valve.
I will check the wiring soon and update you with the info i got about it. From now i suspect th issue to be a wiring issue.
I allso ordered a fuel filter, and i will change it no matter what just in case.
For such an issue i could suspect a catalaytic converter cloggued but the throttle would still open...
I'll keep you updated with my repair.

 

wiring harness checked:
everything is fine

I rechecked the measured values with the diag computer, i am not getting any readings from the Throttle valve, neither from the pedal sensor. Nothing !
The throttle valve has been replaced allready.
I would go by elimination to the pedal sensor, then if it don'T work, replace the ECM.

I will keep you in touch if anything positive or negative happens

 

Thank you for sharing your experience. I sold the car, but I am always wondering what the problem was. I came to the conclusion it had to be the ECM, and did not want to gamble the $1000.

Please let us know how it turns out, I am very curious.

 

We checked the wiring yesterday for the Throttle valve and the pedal position sensor.
All the wiring is ok.

To my experience, 3 things can make such a problem happen:
-Throttle valve (allready replaced)
-gas pedal positions sensor
-ECM

I ordered the positions sensor that i am supposed to get today. If it doesn't work, i'll order an ECM.

If nothing works, then... i have NO idea of what could be the problem.
I have seen such an issue on an e46 325i BMW 2004 4 years ago and after replacing the throttle valve, it turned out to be a faulty DME (ECM in BMW language)

 

First you need to make sure you have the correct Throttle body fitted, also it needs to be programmed to the engine ecu, so that it can learn the idle stop position. Another Used ECU will not crank the engine because the Immobilizer signal will not be correct. You will not be able to do indepth diagnostic work with Generic OBD scanners..

 

Then what do i need to do the proper diagnostic ? My scanner allows me to test the TB and to read measured values on anything i want. It also allows me to do actuation tests on TB or anything i want.

I would like to know the procedure for a TB learnin adaptation, if there is one.

thank you

PS: i changed the TB and pedal sensor allready. My diagnostic is that ECM need to be changed. What do you thing about that ?

 

Problem solved.
Cause: Faulty ECM
I wasn't able to start the car yet but just by pressing the gaz pedal, the Throttle body opens now
I will now see if i can start the car directly from the starter and if it does, i will install an independant switch so the customer can go the the MB dealer get the ECM security reprogrammed.

 

By the way:
That doesn't mean it will allways be the ECM for such an issue.
It can still be the TB or the pedal sensor.
The procedure for such an issue should allways start with the TB and other things around.
The ECM should allways be the last thing to be replaced