[cabmandone]

I wouldn't touch the mixture screw until you're sure your vacuum lines and everything else are up to snuff. Hoses that look cracked should be replaced. Switches should be checked for proper operation. IACV should be cleaned. Manifold boots checked for cracks. What I'm getting at is, make sure things are right before messing with that screw.

I'm going to disagree with proporsche on setting the base idle mixture being yearly maintenance. If your hoses are in good shape, your fuel pressure is right, your injectors are clean and your AFM is working properly, there shouldn't be a need to mess with that screw which is why it's capped in the first place. People pull the cap to mess with the mixture typically to overcome another issue with the car.