Lately I've been seeing my AFR randomly drop to 16's 17's and sometimes even - - - on my wideband while stopped. The car feels like its operating normally and it doesn't do that when the cars in motion thankfully. Anyone know what could cause this? I'm changing my fuel filter/spark plugs/front O2 sensor tomorrow and cleaning my throttle body (again) hoping it makes some difference.

 

cracked flex pipe on your down pipe. Mine was cracked and caused it to read 16's and 17's at idle just like yours.

 

Gaaaay I just changed to a ZZP combo from stock last summer for that exact reason.

 

your fine. does it last only a maybe a second or 2 while at idle? i wouldn't worry about it.

 

its fine. mines done it since day one.

 

Mine does it when I stop for example at a red light after a few seconds. Then I get a check engine light which means "Catalytic converter efficiency low", P0420 if I remember exactly. Then after the check engine light is shown, my AFR comes back to normal.

It seems like the PCM is verifying the catalytic efficiency, doing a kind of test each time the AFR goes lean like that. This is what I understand and what happens to me with the GM Stage 2 tune.

Each time I just erase the check engine light with my Aeroforce Interceptor gauge.

A way that I found out, to avoid the P0420 error code to occur, is depressing a bit the gaz pedal as soon as you see the AFR going lean at idle. Then magic! No check engine light... looks like you avoid the "catalytic converter efficiency test" when you do that trick!