sudden lean air mixture

today i was on my way home and i noticed that my air fuel mixture gauge was showing that i was running a really lean mixture…i literlly watched it running pefect stoichometeric mixture to a really lean mixture…now when i start it, it runs fine 4 about ten minutes then goes right to lean…does anyone know why that it would do that

In my opinion, air/fuel mixture gauges are useless. Of course that opinion is made if you are not using a wideband O2 sensor. The gauge may show you that the engine is going lean, but doesn’t show you how much specifically.

got this pic from here

The purple line shows the wideband o2 sensor while the other shows the regular heated O2 sensor.

Basically, you may need to worry or you may not need to.

Perhaps, if you share more about your beauty, we can give you a better answer. :ok: