What you need to look at is the front Lambda, AF Correction, ECT and rear O2. Comparing the Correction to the rear O2 mainly shows whether the AF sensor is working properly. If the correction is high, positive, and the rear O2 is around .7 V, then there’s a fuel metering or delivery issue causing a lean condition that the ECM is correcting for. That would be a vacuum leak, restricted fuel delivery or MAF, AF feedback.
If it’s high and the rear O2 is high, above .85 V, that’s a definite AF sensor issue.
If it’s low, negative, the engine is running rich and the computer is reducing fuel. That’s a leaking injector, bad FPR, incorrect ECT feedback, or, if the rear O2 stays low, under .5 V, it would be a bad AF sensor.
The intercooler cools the air going into the engine. There is vacuum when there is no boost and boost pressure under boost. That’s why is a vacuum/boost leak if the intercooler is separated. Pulls in unmetered air or it lets boost air out. Either way, the AF Correction will be positive.
