For what it is worth, in 35,000 km of Canadian driving, mostly 3 season, over the past several years with more city driving than highway, I averaged 9.6 litres / 100 km. That translates to about 24.5 miles per US gallon. The worst 5 tank average was 11.2 --> 21 mpg US. I'd have to check the dates but that was likely in the dead of a Canadian winter with mostly short runs to work (8 miles) taking the back roads (hilly @ about 40 mph, some stop and go). The engine would not be fully warmed up for most of that journey. My best 5 tank average is 7.8 --> 30 mpg US on a road trip in good weather, taking it easy, sunroof open, soaking in the scenery. Single tank numbers can be misleading.

The car is a 1990 745 16 valve with manual tranny (4sp + o/d). I am running oversized tires (205-65's)in an effort to keep the revs down on the highway. I am not a lead foot nor a slug, about average. I run regular gas. Emissions testing last time showed high NOx - barely passed. Maybe the cat is on its way out.

Bill
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Volvo Info Site 1990 745GLE 16valve

The B234F gets roughly the same MPG as a B230FT turbo. Your mileage is not unreasonable for city driving. The B234F really doesn't breath well until the revs get up. Depending on how you drive, an auto trannie will probably make city driving worse, but there should be a negligible difference on the highway when the lock-up torque converter gets a chance to kick in. The EPA ratings for your car were something like 18 MPG city, 26 MPG highway and 21 MPG combined. My own experience with the B234F (auto trans) was lower in the city, higher on the highway and slightly lower combined. If you're inclined toward a lead foot, if you use less than the recommended 92 octane or if the engine is in less than good running condition then that will affect your mileage. If you're light footed, using a good brand of gas at the right octane and you're not happy with your mileage then indeed you should clean give the engine systems a cleanout (plugs, wires, throttle body), consider adding an injector cleaner (for one or two tankfuls followed by a spark plug cleaning or new set of plugs) and possibly have the fuel rail pressure checked (in case the pressure regulator is going south). Oh, and I almost forgot, under-inflated, worn or non-stock tire sizes will also affect mileage.
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Dave -not to be confused with a real expert

Well, town driving could be tough. How is it Idling? Also, maybe a Fuel Injector Cleaner like Techron might help some. Hope it helps!
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92 240 2.3 L with a Borla! 103,000 Miles and More!!Go Team Grimace!!