This is the same exact issue that I have going on right now on a '98 explorer sport OHV. But there is no vacuum leaks. The MAF has been replaced. The one thing I have noticed that no one brought up was mentioning anything about fuel trim. Which is funny because when I turn the key on and don't start it the fuel trim is at 100% on both banks. When I take the negative and positive off and touch them together to reset fuel trim, the moment I plug in the scanner and look at fuel trim before even starting the truck the fuel trim is still at 100%. When I start it up, about 1 minute will go by until it goes into closed loop. There is no activity from the O2 sensors. The trim on the O2 sensors read 100%. When you unplug all 3 of them, it doesn't set a code. There's battery voltage to the heater on all 3. There's even ground. But on one of the wires there isn't continuity, which is common on the other connectors.We tried wiggling the harness with no success. The funny part about this story is that when all 3 O2 sensors are unplugged, no MIL is set, not even a pending code.
I'm fresh out of ideas. Anyone wanna take a stab at this?