MOST IMPORTANT RULE OF TROUBLESHOOTING - DO NOT RESET THE ECU
The ecu stores the IAM, AF Learnings, CEL's and knock learning so by resetting the ECU you are erasing all the troubleshooting data.
If your car was knocking and the IAM had dropped or had FLKC all over and you reset the ECU, then you are going to knock all over again until the ECU relearns the knock.
If you had a leak and your ECU learned +25% fueling corrections and you reset the ECU, then your car is just going to run like crap until it relearns the corrections.
Its only a good idea to reset the ECU if you have collected a learning view, made changes to correct your issue, and fully understand what you are doing.
BEST REAL TIME MONITRING DEVICE - WIDEBAND (AEM UEGO)
A wideband is by far the best real time monitoring device for your Subaru. The $165 investment could save you a blown motor and $4000.
Will show you your WOT AFR's. If you were tuned at 10.8 and now your AFR's are 12.5, then you need to start troubleshooting.
At idle and in closed loop a Wideband mounted in the downpipe will commonly show 15-15.2 while the ECU is targeting 14.7. This is common and merely due to the location of the sensor compared to the stock 02 sensor in the header.
Since the ECU is using the stock02 sensor for corrections/trimming to 14.7 this means we basically ignore the wideband at idle....and then at WOT we use the
wideband and ignore the stock sensor.
ONCE IM TUNED WHAT SHOULD I WATCH
Wideband - watch your AFR's if they are more than a full point off (IE went from 10.8 to 11.8) stop doing WOT pulls and start troubleshooting.
AF Learnings ABCD - these are the corrections for the 4 sections of your MAF scale. if they are more than +-8%, start troubleshooting.
IAM/DAM - if the value is less than 1 (32bit ecu) or less than 16 (16bit ecu), start troubleshooting.
Logs - take periodic logs looking for knock, overboosting, out of whack AFR's
Regular maintenance - check oil every weekend, turbo cars burn oil..catch it early. do your plugs at 50-75% of recommended intervals. clean air filters. check vacuum/boost lines (clamp everything). keep meth tank full.