Pull apart this connection (red circle) and make sure you still have the large, ribbed, O-ring on the MAF exit side. A lot of times, it gets crunched up and stuffed in there or falls off which leaves a gap for unmetered air to enter causing the lean code on both banks. If this is the culprit, give the plastic intake tube a spritz inside with dry silicone spray to ease it over the O-ring forming a tight seal