c240 2001 150K miles
Car started running rough, CEL indicated multiple misfires, P0170 and P0173 both fuel trim banks, #5 cylinder misfire. I cleared the codes, bought new plugs, wires and o2 sensors and cleaned the MAF. This cured most of the problems and the car has more power. The problem is I get a slight idle vibration and little bit of delay on take off. The CEL came back on and indicates P0170 and P0173 both banks fuel trim. I unplugged the MAF yesterday and drove to see if any difference. The car was driving horrible with the MAF unplugged. I chugged along a block before I pulled over and plugged it back in. I have searched posts and think it could be a vacuum line or something else???? I could not find any posts relating to finding vacuum line leaks for c240. I read about the $12 hose, but that does not apply here. Any help on how to trouble shoot from here would be appreciated. Any diagram on vacuum lines?

 

I think your MAF is shot. Here are the vacuum diagrams

 

Agreed. Check out my thread Another MAF Thread. I got the same two codes regarding Fuel Trim Malfunction. As Glyn said, your MAF is shot (more than likely).

 

Thanks for the responses, I thought that unplugging the MAF and it running worse meant that the MAF was ok and it could be something else. I will be ordering a new MAF from autohaus. I had replaced it a year and a half ago, so I thought it might be something else.

 

Before buy new MAF, check whether Intake has vaccum leak or not. If there has, it will have similar symptom.

 

Before buy new MAF, check whether Intake has vaccum leak or not. If there has, it will have similar symptom.

 

After you have checked for leaks after the MAF - anything before makes no difference to fuel trim. Please make sure you have the correct Bosch MAF - not some eBay look alike that belongs on an Audi. Because it fits does not mean it is right.

I also note that you have replaced the O2 sensors. Please make sure that you fitted OE heated Bosch O2 sensors. Non heated generics (even if they are Bosch) do not work on these cars.

 

Didn't read the post about checking for intake leak until now. I ordered the MAF insert from german star for $135.00 installed it and took it for a test run. Didn't seem to make much of a difference. I had Autozone clear the CEL. So far driving about an hour, it has not come on. I hope it stays that way. After a little more reading I reset the throttle using the depressing the pedal and key method. Now the lag in takeoff seems to be cured. From a stop it seems to be very responsive. I still have the little vibration in the steering wheel at idle. I will check for leaks tomorrow see if that is it. Should I use carb spray around the intake to check for the leak?

Also, when I took out the maf insert, I noted the numbers on it. old:F00C 2G2 025 and new one was F00C 2G2 032. I don't know if anyone knows what the difference is but I thought I would put it out here to see if anyone has a comment. Thanks again.

 

CEL went off yesterday P0170 fuel trim bank 1. Guy at autozone suggested fuel filter. Ended up changing the fuel filter and cleared the code. I checked and did not find any vacuum leaks. Found out that maf# F00C 2G2 032 is supposedly a VW maf?? I called german star and asked him about it and he said it was for the c240. I don't know if I believe him but it is in and the idle seems to be better. I still don't think it is as smooth as it should be. I will moniotor it for now.

 

Wierd - The MB part numbers for the C240 MAF are:

1120940048 &
1120940148

Make darn sure those are not VW/Audi MAFs - they don't work properly on a Benz - they fit fine.

 

Ragu,

Did you return that MAF sensor? Ever get the correct one?

Thanks,

Tom

 

can some one please explain how this reset for the throttle using the depressing the pedal and key method works exactly.
is the battery supposed to be hooked up still?
and how does it reset the throttle exactly?

 

https://mbworld.org/forums/showthrea...56#post1725156

Calibration between the TPS & the throttle plate can drift over time. Doing a throttle reset makes sure when the pedal is hard on the floor the throttle plate is at WOT.