Hello,

Can anyone give me some advice, I have searched (and read) many threads on this (these) subject(s) but there are conflicting opinions and I thought I might give you all my sequence of events in the hope of advice / a solution

My wife’s 2000 SLK 320 has been running rough for a while, poor pickup from a standing start and a bit hesitant - Having had 3 MAF's in it's life (all under warranty) I knew it was due another and that I would have to pay this time.

At the last MB service they stated it was showing faults and would need further investigation (at £100 per hour !)

I bought a brand new BOSCH item and it was sitting here ready to fit.

3 days ago wife came home saying the CEL was on and there was something hanging down from under the car.

Inspection showed she had caught the wire that leads from one of the lower LAMBDA sensor and pulled the plug apart - Luckily the cabling and plug was undamaged, as were the pins so, having put it up on ramps, I plugged it back together and cable tied it away.

Seeing as I had the tool box out I changed the MAF - 5 minute job.

I then looked at the air filters and they were filthy - I cannot believe they were done at my last service !!!

So, new MB filters were bought and installed the same afternoon.

On the drive to MB to get the air filters I noticed 2 things...

1) - When I started the engine having left it for 2 minutes it started and then cut out as if no idle for first crank and then started fine on 2nd crank ? - Turn it off and start again and every start starts fine unless you leave it 2 to 3 minutes and start - then it will die as if no idle again - odd ?

2) - Having accelerated hard and taken next gear (it is a manual) then car "stutters" before accelerating in next gear. In fact, come off the throttle and let it decelerate for a few seconds then jump on the gas pedal again and again, it stutters before picking up ???

Got home and CEL had not gone off during 3 hours to and from dealer so I disconnected the battery for 10 minutes and re-connected - sorted - no more CEL.

Problems 1 and 2 still exist though.

Any ideas anyone ?

Justin

 

Fuel Filter, Spark Plugs???

 

Thanks for the post but I never touched the filter or plugs before swapping out the MAF and installing new air filters so I cannot see they would start to effect it.

 

Did you read the codes yourself and see what faults they were indicating. After you reconnected the lambda sensor, did you reset the codes and then test drive it to see what codes comes back.

It helps not to toss too many variables in when trying to fix a problem. The lambda wires were one problem so after reconnecting that it might have helped to reset the codes and take it for a spin to see what codes then come up before installing the MAF. You say that it has been running rough for a while so there might be other things contributing to it before all of this. How many miles are on it?

You say that it is a 2000 SLK320? Did the UK get the 320 a year before we did here in the states or would it be considered a 2001 model?

 

Hi

I think it is a 2000/2001 with 60,000 Miles - I do not have the papers with me - it has the indicators in the wing mirrors so it is the 'facelifted' 320.

I wish I had just done one thing at a time also - sadly I do not have a code reader (yet) so I did not (and do not) know what it is saying to me albeit the CEL is off.

With a code reader I hve read the threads explaining you can turn off the CEL and "reset" the error codes but if the ECU is adaptive as it is, can a code reader / resetter also restore those settings to factory default ?

From all the reading on the forum I have done my gut feeling is the ECU has been tweeking itself for the past months to run with the poor airflow and faulty MAF and now they are cured it is not "tuned" to run with the new parts and thus I need to bring it back to a basic "out of the factory" setting ?

JJS

 

With radio code in your hand remove Neg Batt terminal for 1 hour.

Bazzle

 

In regards to your "2 things " #1 CPS - crank position sensor....... # 2 rough idle - O2 sensor(s).Those are the 2 things I would be looking at.

 

Well I got the car fixed and she is running fine now ...

I thought I would post the results in case others have the same problems.

I asked the MB technician before booking in the car what he would look for and he asked, if you unplug the MAF plug does it stop the faults ?

I replied, "Yes" and he explained that by unplugging the component the ECU sees a fault in the circuit and runs the engine on a basic "default" level of engine parameters, some people call it grandma mode but to be honest the car drove fine, just a little lacking on power but not exactly grandma !

This would be his indicator that the MAF was at fault and his first starting place.

He did say it was possible that the engine had "trimmed" itself over a period of time to run with the old, not so good, MAF and dirty air filters and that now they were replaced the "trimming" was causing the poor running. Left alone he said it would slowly trim itself back to cure itself but it would take a VERY long time.

He explained that he is able to load a new "boot strap" which basically sets all the ECU trimmings back to basic as if it had just come out the factory.

This cannot be done by removing the battery as they are stored in the EEPROM, also a basic OBD cannot set new values, only clear fault codes.

In other words, I had to get MB to do it or find someone with a top of the range MB diagnostic machine - Not very likely !

But, this begs the question, how come my brand new, boxed BOSCH MAF did not work ???

An "out of the box" failure ? - Again, Not very likely ?

I have read another thread from the US where the driver had exactly the same faults after buying a new MAF and he ended up buying another new MAF, this time from MB to cure it !

Well the MB tech took it out on a road test with the laptop plugged in and it said "MAF Fault" - He got a new MB one off the shelf and fitted that and it was cured !

So, I looked at my new BOSCH MAF and his boxed MB part and THEY ARE IDENTICAL !!!!

They are both exactly the same, same part numbers, bosch and MB parts numbers on both, the one I bought someone suggested might be a fake but the thing came from a reputable company and it is 100% identical in every way...

...
except one
....
When you look at the electrical plug on one MAF it has B1 printed down inside by the pins.

When you look in the other it had A1 printed ?

That is the only difference.

My conclusion, Mercedes buy in MAF's from BOSCH and do something to them to make the give different values so a NON modified MAF will not work properly and thus you have to buy one from MB.

Call me suspicious but I think that is the answer.....

Any MB or Bosch people reading this.... Come on, spill the beans

Justin

 

Good post. I had a very similar experience.

Bazzle