W639 115 CDI MAF Mystery Any help greatly appreciated!

[Nathanjennings]

Hey guys. Had my 07 Vito for around 4 years its done 184,000 and an absolute beast still.

Although I'm having some problems with the MAF. In low gears the, especially 1st gear, the van jumps and jerks like it cant breathe properly.

Connected a OBD with live data and the MAF data was erratic, spiking and dipping uncontrollably. Also at idle its spiking to 40g/s - 60g/s which is ridicuously high.

Replaced the MAF with a cheap aftermarket one and the problem was even worse. Replaced it with a genuine part from a breakers yard and its much better but the problem is still there. When the MAF is disconnected the van runs like a dream albeit with slightly less power and obviously worse fuel economy. What's strange is the OBD tester was still showing MAF data whilst it was disconnected. Any ideas?

I've tested the wiring harness I'm getting;
Pin 1 - 5v (IAT?)
Pin 2 - 5v (Signal?)
Pin 3 - Ground
Pin 4 - 12v

Could I be super unlucky and have gotten 3 bad MAFs in a row?

Any help is greatly appreciated, It's driving me nuts!

 

[supernoodle]

Certainly 40 g/s isn't correct for idle. It's impossible. Something about 15 g/s is resonable, closer to half that if EGR is active. There's always a chance the tool is wrong of course.

I posted a rough calculation here before https://forums.mercedesclub.org.uk/index.php?threads/what-if-you-maf-reading-in-g-s.192963/

I already commented in one of your other threads where you say you had MAF and IAT errors (and EGR flow but that's based on the MAF), you'd be unlucky to get both fail....But as you've pointed out, they are combined as a TMAF, they share wiring and looks like a common ground. Given that it's unlikely to be the sensor as you've replaced it several times, I would focus on the wiring.

Unfortunately the MAF signal is a variable frequency signal, so you need an oscilloscope to look at it. A decent auto electrician should be able to do that if you're still stuck.