C Holmes: Are you comparing oxygenated, and non-oxygenated fuels? Most pumps will tell you. I had a 91 Volvo 940GLE that wouldn't run happily on oxygenated Amoco premium. This was the only kind of gas available in Northern Virginia. As soon as I filled up a couple tanks in Pennsylvania, again with Amoco premium, the idle cleared up.

Perhaps you have carbon build-up in your engine? Maybe try to run a couple bottles of Techron through it and try an "Italian Tune-up"...

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Bob Roe
Lehigh Valley PA USA
1973 Olds 88, 1972 MB 280SE, 1978 Datsun 280Z, 1971 Ford T-Bird, 1972 Olds 88, 1983 Nissan Sentra, 1985 Sentra, 1973 230.6, 1990 Acura Integra, 1991 Volvo 940GLE wagon, 1983 300SD, 1984 300SD, 1995 Subaru Legacy L wagon, 2002 Mountaineer, 1991 300TE wagon, 2008 Murano, 2007 R320CDI 4Matic 52K, some Hyundai, 2008 BMW 535xi wagon, all gone... currently
2007 Honda Odyssey Touring, 2014 E350 4matic