Kickdown issue

[W202 MAN]

Hi Guys just wondering if i pick all of yours brian for knowledge a sec, i have an issue with my kickdown its a bit strange. ok i have my 98 c200 in s mode on the transmission and when i kickdown for overtake its changes down but will not go above 4000rpm and 60mph, i took it to my trusted merc mechanic and he read an error code of the car as 02 sensor failer and the car is running lean. Now here's the thing if i accelrate normally and i just press the pedal down quickly it pulls amazing and goes well passed 4000rpm and i can also do this shifting manually, doesnt feel like any performance issue.

So am puzzled :confused: is the o2 sensor really faulty or is it the dredded MAF sensor, has anyone else had this? Thanks

[zmatt]

In our cars 02 sensor = MAF sensor. It means mass airflow. luckily its the easiest thing you can do under the hood. what model 202 do you have? most models have it not too far down the pipe form the throttle body. It's a black tube with a wire coming out of it, it's pretty obvious. There are clips on both ends that you undo and then you just pull it free. the wire is probably zip tied to the rest of the intake so just cut those ties.

The MAF looks something like this;
http://www.diymyride.com/wp-content/uploads/2011/03/boschmaf.jpg

Its little more than some simple circuitry and a connector to the wire loom ass in a plastic tube. Pretty simple tech actually. A lot of people have good results gently spraying the element on the inside with their favorite multipurpose lubricant/cleaner like WD-40 or PB Blaster. If the MAF is just dirty then that will clean it up and after you have the code cleared you are in business. If it is actually damaged then you need to buy one.

A shot inside the MAF, that brown thing is the element that actually detects the air mass. This one is a different version so it doesn't look exactly the same. but google, whatcha gonna do?
http://12v.org/urs/AANvsRS2MAF.jpg


Also a good thing to know, the BOSCH sensors are actually pretty standard so if you can't get one for your model you can get one form another BOSCH equipped car, for example I replaced my MAF with one from a land rover cause I could get it cheaper. The tube was a different diameter, but I unscrewed the sensor and put it in the old tube after cleaning it. Worked brilliantly.



Here is a writeup by some afla owners about it.
http://www.guzzimental.com/afm%20about.htm

The BOSCH MAF appears to be standard on VAG products and on Alfas as well.

[W202 MAN]

Thanks for the information its massive help. i wll have a go at cleaning the MAF before it goes into the mechanics just in case i can fix it like that. thanks again

[zmatt]

no problem, btw the lack of power you are getting because of that is likely limp home mode. It cuts power pretty drastically when it reads a fault like that. Also to see if it worked you can clear the code by unhooking your battery for a few seconds. Your power windows will act silly for a it and you will have to re-enter the code to your radio but the code will be gone.

[Spikes]

no problem, btw the lack of power you are getting because of that is likely limp home mode. It cuts power pretty drastically when it reads a fault like that. Also to see if it worked you can clear the code by unhooking your battery for a few seconds. Your power windows will act silly for a it and you will have to re-enter the code to your radio but the code will be gone.

Thanks for that clear explanation of the MAF and the pointers for replacements!
Spikes

[W202 MAN]

Got the car to the garage, major MAF sensor fail the car started to go eratic on the idle, got the new 1 installed £240 later and the car is like new with alot more horses available it seems :)