Hello everyone, really hoping you can help me out here...
I've got an 07 GTI that I'm having some troubles with, namely a lean code P0171.
I have previously checked for vacuum leaks, of which I didn't find any, got the garage to do a smoke test on it, which revealed a boost leak at the throttle body. This was rectified at the time.
I have since purchased a genuine VAG-COM cable to do some data logging and try to diagnose the issue myself.
After reading many, many forum posts both here and other sites I have learned that the MAF readings should be around the 160 g/s mark (?). The car is standard apart from a Forge intake, Scorpion cat-back, and GFB DV+.
I logged the MAF readings and discovered that the MAF was reading really quite low, 100-110 g/s at full chat in 3rd gear. So with this information I ordered and fitted a new, genuine VAG MAF at the eyewatering cost of £164
and it didn't fix the issue. Still running lean. Long Term Fuel Trims are through the roof, pegged at nearly 25%, Short term is with in spec, normally sitting around 2-3%%.
I've also recently changed the pre-cat oxygen sensor, at the recommendation of the garage who done the smoke test. I had recently had it back at them to help diagnose, but all they done was reset some adaptations rather than perform any proper diagnosis. (I had explained to them before I left them the keys that I had replaced the MAF and mentioned the fuel trims).
Anyway. This is leading me to believe the culprit is the wiring from the MAF to the ECU is the issue, as the new MAF is showing similar readings to the old one. Could the wiring be an issue, even if I've not got a code for "implausible signal"? Is there something I'm overlooking that could be causing the MAF to read low
I'd really appreciate any help that you lovely people might be able to provide.
I've attached an excerpt of the log I done on my way home from work this evening. WOT in 3rd gear showing my low MAF readings. There is other data on the log too as I had read a post from Pudding from a while back on another MAF issue and hopefully these will help confirm a diagnosis. I'm a wee bit out my depth here ngl...
