Even running the 91 tune will make a noticeable difference over the 87 tune. I wont run the 87 tune anymore. Does your car rev up for a bit when you turn your car on first thing in the morning or when its sits for a long time on the 87 tune? I always wondered mine did. It doesnt do it on the 91, yet it will lean out bad if I dont warm it up first. Anyone one else expirancing the same thing?