how lean is too lean

[satur9]

i running a narrowband. but this problem has been driving me crazy. so im gonna buy a wideband. but anyway . my car has been running lean lately (about a week) from what my gauge says. its not reading as high as it used to and it used to run rich at wide open throttle but now its just in the middle.the last time this happened a bottle of fuel injector cleaner fix i guess were dirty injectors.it didnt work this time.funny thing is the egts are and have always been at around 1200(cruising) .my question is will or can the stock ecu self correct this and if it is running lean. will continued drivivng mess up my engine.cause it runs fine and egt is normal im just wodering if it might be the o2 sensor going bad but shoulnt the ecu throw a cel light if it was .

[Celicasaur]

Could be any number of reasons, but my initial guess is with the maf maybe needing a clean...no wait, a dirty maf, runs rich, right?

Possibly a vacuum leak somewhere in one of the pipes around your intake, TB or IM...that sounds a better explanation for something as sudden as this.

[GSBoek]

A dirty MAF will make a lean run, it's reading less oxigen than there is actually going in, so you endup with less fuel, more oxigen=lean