whats wrong if car running to lean and how to fix it

 

A bit more info would help, Management, Car, Engine etc

 

it depend when it is running lean

AFR around 15 on idle and slow drive can be normal, if it happen when accelerating then it can be for examle, poor fuel pump, too low fuel pressure, damaged AFM/MAP, engine modyfications without mapping

 

Means not enough fuel, will kill the engine in time.

Steve.