JNeidlinger

Driving my car like normal. Stop at a light. Notice the car seems to be idling a bit low if I have my foot on the brake. Think nothing of it, barely noticeable. Press the gas to go, engine dies, ESP error comes up.

Put it in park, remove key, re-insert. Cars starts back up, I get it to the closest parking lot.

Throttle responding weird. Press the pedal at varying angles and the engine just idles... but intermittently responds and revs. Turn off the car for a bit and do a TPS reset.

Check engine light is on, and I run the scanner, get P0120 Throttle/Pedal Position Sensor/Switch A Circuit Malfunction. OK I guess.

After resetting the TPS I get the car home without hiccup. Later that day I take it out, and the idle is just strange. When I come to a stop, the idle will not be at its normal ~600 RPM, but rather too high. Sometimes it sits and idles at 2000 RPM, sometimes 1000 RPM. Sometimes if I turn it off and back on these problems go away (for awhile).

Well, P0120 Throttle/Pedal Position Sensor/Switch A Circuit Malfunction would lead me to believe I need to change the Pedal/TPS assembly.

What do you guys think?

Oh and PS, I encountered the dreaded CPS failure about 1.5 months ago, it completely went out. Replaced that and all those related issues went away. Wow, replacing the CPS was one of the most frustrating thing's I've ever had to do on a car, sensor related.

C32maximus

I am going through the same problems on my 2003. Search the forums by ESP and codeP0120 to pick up my thread and many others for more info. Best to get the car scanned with a star system to help pinpoint the problem. The code is very generic and can lead to a lot of parts replacing if you start to guess. Pedal replacement, throttle body, wiring to throttle body, engine wiring harness, steering angle sensor are the common fixes. On my car the dealer wants to replace the throttle body but will not guarantee that it will fix it. I am in the process of installing a used throttle body and will report back after I finish next week. Good luck. I replaced my pedal with a new one and nothing changed. Just thought I'd through that in.

johnng117

It happened to me today, my idle is unstable again, if i gas the rpm increases and stay there, so if i gas it to 3000rpm it will stay there tben start hunting. Very scary.
Ive changed wire harness, TB, TPS, reconditioned the ECU, still giving me problems. The star keeps pionting to the TB, but this item has been changed 3 times now.

JNeidlinger

I realize this is a very old thread, but I thought I would update this, as this seems to be an extremely common problem symptom wise.

This has completely been fixed!

What was wrong? The throttle body wiring harness connector NEEDS TO BE CLEANED / TIGHTENED.

I was SO close to replacing sensors, buying a costly replacement throttle body, etc.

My guess is 95% of other people experiencing similar issues simply need to check this connection / clean the connector.

I used some electrical contact cleaner, and sprayed the inside of the harness connector, and the plug on the throttle body, and then used some silicone grease when reconnecting. Problem completely gone, now idles PERFECT no matter what.

C32maximus

I wish my problem was that simple. I cleaned and tested my harness to throttle body connections. In the end I replaced my throttle body with a used E55 one. Problem was gone on startup. I had the car scanned by Mercedes and it pointed to the throttle body. I didn't believe it at the time but it did fix the problem. The used E55 TB was only 200.00 on ebay.

c32used

Is this the connector to check and clean?

It wasn't clipped on to metal clip as it is now. Now held in place tight.

c32used

All I did was removed and reconnected and fine since.......THANK YOU!!!!!!!!!!!!!!!!!!

c32used

Ok has not returned and driven car 150+ miles since...talked to Konrad of Speedriven in Palatine IL and he said this issue is not uncommon just they haven't seen it on C32 much I was fortunate the code P0120 can up and I tried this first.

joc

I had the same issues and this is what I found
1.with car running and idling up and down sprayed carb cleaner around air intake at the rear where the two rubber gators go over the filters to the air intake throttle body. Every now and again idle would even out, this proved that there was some air leaks around the rubber intake boots.
2 after some real close inspection I also found the air breather tubes from the valve covers had a small crack due to hardening on the underside.
3 I purchased a new air intake adaptor with the two rubber boots and at the same the two rubber hose connects to the valve covers.
4 took all filter off cleaned everything, cleaned the throttle body, it was real dirty. Re fitted the new hoses to valve covers , this is a little awkward, fitted to air intake boot assembly again this was not easy needs some patience DID not have the steel clamp bands so used black wire ties. you can't see them so looks great.
5 started up and idle is great no hunting or ups and downs.
6 it was very hard to see any leeks so you need to us carb cleaner and listen it finds the leaks
Hope this helps.
John

c32used

Was this a permanent fix for you?

c32used

We today I remove whole air intake system cleaned that and throttle body. Started car up and idles normal again. I'll post if issue returns but only cleaned did not replace anything.

joc

To answer your other question yes it solved my problem.
Hope all works out well
Thanks
john