P0505 is a code I've never seen. I'll deferrer to our local experts here. However, I would remove and clean both the air idle valve and throttle body. The air idle valve should clack when turned over back and forth. Brake cleaner or carb cleaner work great on it. The TB should only be cleaned with specific throttle body cleaner.

For front O2 readings, you need a graph to see its operation. Max voltage should be 0.9V to 0.2V and oscillating up and down. For rear O2 readings, voltage should be steady for each idle RPM. The last Ford Escape I looked over for a friend had 0.7 volts at idle. I would up up 0.8 at 1500 RPMs. As long as voltage was steady, the engine is running great.

I learned the MAF sensor trick from here. When unplugged, the DME uses a default fuel map. The fuel map should be ideal conditions for it to run properly. Sounds like you need a new MAF sensor to fix some issues.

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'06 X5 3.0i - bought @143,123 miles (12/26/20)