AMF Airflow Oddity

Dsldude

Member
My car is actually a Polo 1.4 TDI but people on this forum seem very knowledgeable on the 75 AMF engine.

I recently swapped out a faulty coolant temp sensor as the dial on the dash was waving at random,
after doing that I thought I would use VCDS to check the new on was reporting the right temp to the ECU.

I did a routine scan for error codes and it picked up 16485 - Mass Air Flow Sensor (G70): Implausible Signal.
long story short I replaced that with another genuine one and that error has not comeback, but the airflow oddity was there on the old Maf aswell.

While using VCDS I noticed something doesn't seem right with the airflow, I took the car for a good blast and logged some stats in VCDS, What doesn't seem right is at idle it can draw about 200mg/str of air according to the MAF but then at say 2000rpm it says its using less air at 190mg/str, even when I was flooring it at about 3000rpm in 3rd it was pulling up a hill great and boost showed about 2300mbar, yet the MAF said it was using the same or less than the amount of air at idle.

Couple of other things I noticed is EGR duty cycle never goes above 20%, and EGR Gas actual is always below EGR Gas specified, for example at 3k RPM EGR Gas specified was 1000mg/str yet actual was only 200mg/str.

Boost seems to be ok looking at requested vs actual and the car drives fine in all respects good power etc, I dont want to mess about too much looking for a issue that is not there but if something is not right and its worth fixing like a little more MPG I would like to do it.

I took the EGR intake pipe off to take a look it was cleaner than I expected after 155k miles, the EGR exhaust valve was closed at idle so I cant say for sure its opening as normal but its not stuck open.

I have attached the vcds log as a excel file inside the zip folder, if anyone could make more sense of it than me or share with me what is normal for these figures when you check your AMF engine in VCDS.
 

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Last edited:
Dsldude,

This
website gives details on the units for the MAF reading from VCDS, you need to convert mg/str to kg/min and if you do this using your data the figures look to be fine with flow at idle around 17kg/hr and 56Kg/hr at your highest engine speed.

Hope this helps, I can't shed any light on the EGR though.

Steve
 
Hi Steve.

Thanks for your input and sharing that knowledge.

I think I should just put the spanners down and walk away now :)

I guess even if the EGR is doing something funky it really doesn't matter until it
affects real world performance, I get about 50mpg town driving and it passes the MOT
and I dont feel it driving any worse to when I got the car in 2004.
 
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