Probably what happened was the computer noticed that readings were way off from what it usually gets. So it went back to closed loop operation: basic internal program designed to keep the engine running and get you home. Disregarding feed back from the O2 sensor. Sort of flying blind.
I think that this is actually called "open loop".
When you are receiving feedback from the sensor and adjusting based on that, you then "close" the feedback loop.
Open loop is seen at startup and in "limp home" mode and various other times.
i thought i reset the ecu after i did the maf, then test drove it to the bank, and it ran like crap the whole time, probably running rich as hell, then i got home, re set it again, and tried tracking a vacuum leak, so the engine was running for a good 30 minutes there. plus me "testing" out the housing used up a bit more gas.
i put in 87 octane like usual, and am driving normal again. i do need to check the tire pressure though, im pretty sure its a bit low.
1000 bucks for instant 400% mpg gains :
"This is a 1995 Geo Metro
3cyl.Standard. It is a very basic car just has power steering and CD stero."
Yup. Seen plenty good things here re. the Metro series. One version is built for even better FE than the rest. FX trim maybe? Of course the usual caveats are in force: may need work, ymmv, no guarantees, etc.
Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.