98 Ford Contour v6 2.5L

PLEASE HELP!!! I'm at a complete loss with this car....the P1131 won't go AWAY. So far I've cleaned the whole air intake out including the MAF, changed all the hoses to the air intake, changed air filter, changed gas cap, changed fuel filter, 6 spark plugs, oil change, oil filter and o2 sensor (Bank 1 Sensor 1) which is what the code is for. That that o2 sensor has insufficient switching from lean to rich and vise versa. So.....please what else could it possibly be?? Yes I have cleared the code by the odb11 and by disconnecting the battery. The check engine light just goes on anywhere between a couple times of driving throughout the day or it'll take a day to go on. It's still that same code! At acceleration I do feel as though I'm losing power. Even though I did all that.