Open the hood and try to hear for a hissing air sound. It could be as simple as a vacuum hose broken but it could be others too. You might want to read through the TSB below for a full diagnostic of the P1151 and other codes.

http://www.v8sho.com/SHO/TSB0197HO2SServiceTips.htm

Good luck.

"Always do the cheap and easy ones first." 1996 V6 ATX 96K miles