1) The Accord (in signature below)--never used a fuel additive. I put a lot of highway miles on and buy gas wherever has the best coffee. Would Redline be the best to start using--full bottle initially and then maint doses? 2) The 4Runner--high miles, probably never had a fuel treatment, runs good but occasional rough idle (and of course poor mileage). Would Redline be a waist of money...at least until I've done the full Seafoam treatment (into vacuum hose, etc)? Is there any potential harm in doing a strong Seafoam treatment to such a high mileage (and potentially dirty) engine?