Erratic idle on cold, Not maf NOW solved!!

[mick777cpt]

Hello Guys

Just for info for those searching for MAF problems. I have a 2001 W203 C200K with 97k Miles. For the last year when the car has been left for longer than 12hrs, especially when cold it has an erratic idle on start. You have to put your foot on accelerator for the first 2 seconds as it sound like it might cut out.

Very Occasionally (every other month) the ECU light would come on and after investigation with my own tester it was always the MAF that had the fault code. The car had no other faults. Drove perfectly after start and kickdown was perfect.

I bought a brand new MAF from Merc and it is the Siemens type and not Bosch. Tried it and still no change and the ECU fault light was for the MAF again. In Dec I sent the car to MERC for investigation witht the new MAF and the ECU light on. They confirmed the fault CODE was the MAF but the car drove fine and the MAF was not faulty. They tnen took the throttle body apart and found it to be in a very dirty condition. They cleaned it all out for me, refunded the MAF and since then the car has been perfect. Started this morning at 5am temp was -5 and Sweet start with no foot required.

I put this on for info really, as sometimes these Electronic cars are not as clever as we all think. If you have problems like this save the money for the MAF and clen the throttle body out forst to see if that helps.

Regards

Mick

 

[BlackC55]

This is good advice as I had a car in recently (A160) 168 chassis with a MAF fault. The cure was a thorough clean of the throttle flap. The MAF was fine.

 

[Autofix]

The symptom and fault you describe logs a code for MAF plausibility rather than just a MAF code.
MAF plausibility is the ECU checking the air flow signal level versus engine speed, throttle position and boost. In this case the signals do not match because the throttle is not closed as much as it should be due to the carbon/oil mist build up around the butterfly valve. Looking at freeze frame data is a dead giveaway for this one.
The only problem I can see with doing this DIY is that the throttle position has to be relearned after the t/body has been cleaned.

 

[mick777cpt]

So how do you re-align the Butterfly valve?

 

[Autofix]

This is done serially, ie with a diagnostic tool. As far as I am aware very few, if any, aftermarket tools will do it. Star tester obviously and a tool called Autologic will do it.