I wouldn't go with a higher octane it won't make a difference. I think the #1 thing to do with older vehicles is to pre-test. It can save you from becoming a gross polluter which is like going to hell in a handbasket. If it passes on the pre-test the tech will run the real test, if it doesn't he can abort it and you can resolve the issue. There is a sticky thread around here on one of the sections with a lot of good info in it.