I drive an IS 500 very seldom at the moment, about 4 miles a week.
I have E10 premium gasoline (10% Ethanol) and about 90 miles of gasoline left, so about 1/3 my tank.

My question is, can I safely add fuel stabilizer to my car?
Should I do it at all, or will it not make a difference?

I was looking at the brand "STA-BIL"

 

Yes it's safe to use. How long ago did you fill up? If your tank is lasting longer than 3 months or so then I'd fill up and use Stabil.

 

1.5 months ago

 

A near empty fuel tank provides a larger area for condensation to build up. Sta-Bil is good but not necessary unless you’re storing the vehicle for a long time…months. SeaFoam is a worth while additive as well.