Extreme fuel consumption... HELP... Code 51- Bank 1 Lean

My '96 XJ started running pretty bad about a week ago. It is using a LOT of gas. Its pulling a Bank 1 Lean code (Code 51) but Im not sure what the culprit is. Apparently it is thinking that its running lean and adding a TON of fuel when it is actually running rich to begin with. Does anyone have any idea what the prob could be? I was thinking o2 sensor or something of that nature. Wondering if anyone has experienced this problem before.

Thanks

maybe the map sensor ???

this is exactly what happened to me. see a lot of these posts but noone seems to have found the problem. Code PO171.
http://www.naxja.org/forum/showthread.php?t=19632&highlight=po171

checked it with a scan tool. o2 sensor readings looked fine. map sensor readings looked fine. maybe a stuck valve im guessing. going to do a compression check later today.

haven't touched it today yet. any suggestions?

was the MAP sensor. cleaned it out with some carb cleaner then hit it with some air. had to replace the TPS and idle air after swamping it seems to be running great now.