Making sure that all fuel mixture input sensors are functioning correctly is always a good thing when you have a fuel mileage concern. If the engine runs too rich, it will consume raw fuel at a faster rate than it is supposed to. For example: If the O2 sensor is malfunctioning and tells the ECU that emissions are too lean, you will have a constant rich mixture.

I have an 86 740 with the B230F and I've been averaging 17mpg in the city and about 25mpg on the highway. I don't know what the factory sticker originally claimed the fuel mileage to be, though. I would highly suspect that your extreme case would most likely be a mechanical problem in the fuel tank itself. I would agree with the previous posters. What I pointed out would be for less extreme cases, but I would definetly check out your fuel mix inputs as a secondary approach.

The shimmy in the steering wheel when braking...I would check your strut rod bushings. These bushings aid in keeping your wheel assembly from moving towards the back of the car under braking loads. If they are bad, you will experience this shimmy or in more worse cases-shuddering. A visual inspection of these components can be done. But, according to most bricksters they are in need of replacement at 100000 miles. Hope this information is helpful. And as always, for further information about these or any other symptoms/ problems.....use Steve Ringlee's FAQ or the archives.