Larry, pick your poison. Yes, there is evidence that most of the major brands have detergents whaich are alledged to keep the injectors clean. How effective this can be is questionable. If it were 100% true, then there would be no need for injector cleaning additives. If your brand of fuel is one of these and you notice your performance dropping or rough running, then the additives aren't doing the job.. I have used STP injector cleaner with an improvement in idle and startup, but, having said that, I guess mine were pretty crummy. All gasolines produce varnish when heat cycled. I used two bottles on a full tank and have never had to repeat the dose. Also added some dry gas as well. I don't think there is any exact science here. If I could get some of the aviation gas they used to use with the piston type aircraft engines, I'd use that as well. There are two trains of thought on octane. High octane numbers retard flame propagation within the cylinder thereby preventing ping or knocking at the expense of less complete combustion. Lower octane numbers burn more readily, but are prone to the above. I have used regular unleaded in my 300 for over 5 years with no ill effects, ie. no pinging, knock or plug telltales. Mileage can be as high as 26 or so w/o leadfooting. I had the emissions checked by a local garage. There is a difference, albeit slight, when running the regular unleaded, CO was lower (can't remember by how much, but was lower). This was a bit of a digression, so, cutting to the bottom line, try the injector cleaner. There doesn't seem to be a downside to using it. Just my $0.03 worth.
2000 Dodge Grand Caravan SE