running lean issue

[Ryokai Fuji]

my ka24de runs lean on idle, the o2 sensor locks at .8v at idle. the car has its power. the car runs fine at cruise, the o2 sensor starts to fluctuate from .2v to .8v like its suppose too. any ideas on why it runs lean ? thanks

[S14DB]

Narrow Band sensors are worthless for diagnostics. They only read a little over and below 14.7:1 for fuel trim. Hard to say you are running rich or lean off of it.

Use a wideband sensor to see if the car is really running lean.

ECU usually trys to be as lean as possible at idle for emissions.