Where to start?

[mbeach]

Internet copy/paste about your HO2S (heated oxygen sensor) code:
Electrical:
-Water in the harness connector
-Open/shorted HO2S circuit
-Corrosion or poor mating terminals and wiring
-Damaged HO2S
-Damaged PCM
Fuel System:
-Excessive fuel pressure
-Leaking fuel pressure regulator
-Low fuel pressure
Induction System:
-Air leaks after the MAF
-Vacuum Leaks
PCV system:
-Improperly seated engine oil dipstick
EGR System:
-Leaking gasket
-Stuck EGR valve
Base Engine:
-Oil overfill
-Exhaust leaks before or near the HO2S(s)

These pretty much highlight what the other board members have clue'd you in to. Triathelete's loose gas cap causing low fuel pressure, Maugan's bad FPR causing low/high fuel pressure, vacuum leaks etc.
I cut out some of the more odd scenarios (like running out of gas).
Just run down the list and see what's what.

I'm a big fan of using a can of carb cleaner to find intake leaks. I think that'll be the root cause of all of your troubles.

[mbeach]

That PO140 code keeps coming back as a dirty/clogged EGR valve. Search the cleaning procedure here -it takes 10 minutes and uses the same carb cleaner that will help you find your intake leak.

Also, most of the MAF issues that I've found can be fixed by a simple cleaning of the contacts with some electrical contact cleaner and some elbow grease.

[Tone]

I also recommend the 2 combination ODBII gauge units that read and reset codes that let you monitor quite a number of variables live while driving that can alert you to potential issues. Square Scan Gauge that sits on the dash is $125 delivered and the 52mm round unit for pod mount, it $249.00 - email me for more info if questions not answered on the lower left of .info home page.

[SGT.BATGUANO]

check the maf connector, unplug and replug. might want to pull the maf and inspect. check all injen intake hose connections for leakage. do you have an oilable air filter/ is it over oiled?

It looks like one o2 sensor may be bad or have a wiring problem. judging by the codes it doesn't seem too complex a problem or expensive to repair.... unless other codes show up. your orig. post said it had 5 codes.