My 2007 Sienna with 140k miles has been throwing codes for several months and so far all my repairs have failed. I will start by saying the car has been well maintained with a full tuneup at 120k including ND FK20HR11 and new ND coils for all cylinders. The van started dying intermittently at idle usually after being started which resulted in a P0300 (Generic misfire) code. At this point the MAF was replaced and the problems disappeared. Later in October P0300 appeared again followed by P0174. At this point I checked vacuum hoses and for leaks in the intake system. Cleaned the throttle body which had been cleaned before. Code P0302 (Cyl 2 misfire) and P0300 appeared. I took the van to a mechanic and he recommended all 4 Air Fuel sensors be replaced. All 4 sensors were replaced with ND sensors. The problems persisted with additional P0302 codes generated. while checking the system I found a loose ground on bank 2 and thought I solved the problem but soon the misfire P0302 reappeared. I figured the problem could be in the fuel system so I checked the fuel rail and noted cyl 2 injector not firing as good as the others. Replaced 3 injectors on bank 2 with rebuild ND injectors. Now I have code P0174 multiple times and My Innova 3100F reader indicates intermittent 0 voltage on the Bank 2 Air Fuel sensor and suggests it be replaced. The sensor was previously replaced with ND 234-9049. The van dies intermittently at idle and then exhibits lack of power. Shortly after this occurs it starts normal and runs great with lots of power. Could this Bank 2 AF sensor have failed or was I sold a bad sensor? Any help resolving these issues would be greatly appreciated. P.S. Replaced the Bank 2 AF sensor with a new ND sensor but this did not solve the issue P0174 reappeared. I am at a loss as to what the problem is.