My 1998 GALANT KEEPS SHOWING A P170 OBD CODE?

Looked up Means fuel trim malfunction bank 1. I have just about replaced everything there is except inside engine components,over the course of the years,i have done regular tune ups,changed oil,replace o2 sensors, plugs,and checked all vac leaks contiuously . it is running lean aparently. Is this a bad matter or can it be over looked and if so what is the worse that could happen,runs fine,except once n a while it wants to hesitate when first start up and push the accleratro to get out of my drive way,after that is fine,I have replaced m air flow sensor as well.