I tried to rule out any issues with hardware/software, as I get the same range of extreme readings whether I use a Kiwi2 Wifi adapter + DashCommand app on iOS to read SAE.LONGFT1, or a generic ELM327 Bluetooth adapter + Torque app on Android. If I immediately change over to reading generic the OBDII PID 0x0107 'Long term fuel % trim-Bank 1', I'm getting trims that change every second or so and vary betwen +15-20%, solidly in the bad range. These readings seem normal enough, and I show no DTCs being thrown by the engine.
VAG-COM + VCDS readings from engine block 032 give me idle trim +1-2% and partial throttle trim +4-6%, and they change very little over time, and change slowly when they do. The problem is that I'm getting wildly different LTFT readings when I use a generic OBDII interface versus my VAG-COM interface, and I'm hoping there's some obvious explanation like 'the ODBII PID can't be trusted so ignore it'. I'm trying to diagnose some rough idling and sluggish start issues (stock everything except GIAC Stage 1), and I'm looking at my long term fuel trims to see if it's a symptom of other issues.
