1997 Ford Explorer Sport AWD. While driving the 4WD and 4WD Low lights flash. About 6 times or so. Then goes away then comes back. And when at low speeds Around 20-45 it jumps/hesitates. I Replace the Tpi?? Or tps sensor on the Idle air control and it stoped jumping BUT when taking off it sucked. So i got 2 from the junk yard/ Salvage yard and either one stops the jumping but it goes real slow when taking off. But the other one jumps bad and then it has great taking off speed. What does this sound like to you? I Just put new Spark Plugs in it. Also Code P1506 Keeps coming up. Thanks allot. Also it is not the spark plugs cause it was doing this too before i replaced them. Thanks