940 Turbo Gas Mileage - Air Cleaner Case

I wrote several months ago about the miserable gas mileage I get from my 1994 940T (automatic) Wagon. I still get about 14-16 Miles per Gallon in
the city and up to 22 MPG on the highway. This is far below expectations, and feedback from the group suggested that something was amiss - probably vacuum or turbo hose. The Volvo specialist that has worked on the car for years shrugged his shoulders and told me that "it is what it is - There are no adjustments - If there was a vacuum leak, the CHECK ENGINE light would be on.
The Volvo dealer told me to go find the highest price premium gasoline I could buy and use it. Premium gas did get me about 2 MPG, but it still seemed way too low.
Tonight I discovered that the plastic case that holds the air filter has not been properly closing. A previous owner (or mechanic) had broken off the clamps that hold the two pieces together. Instead of the clamps, sheet metal screws were used to hold the two pieces together at the four corners. One of the screws had stripped out of the plastic below, and the tension from the air filter gasket had opened a seam between the two pieces letting in large volumes of outside air.
My new theory is that this outside air is not welcome, and that the O2 sensor is getting a false reading - telling the fuel injection system to keep adding gas to the "lean" air mixture it sees created by the breach.
I have re-sealed the box (using a new screw) and will now run a tank of gas through to see if there is an appreciable difference.
Am I dreaming or does this make sense?
Dave in Oregon
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are
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The airflow sensor is after the airbox so the leak shouldn't effect fuel economy, it's certainly not good for the engine to be breathing in all that unfiltered air though.
How's the tire pressure? That can make a big difference, it's also worth checking the plugs, cap, rotor, wires, and timing. I would expect closer to 25 mpg on the highway, I find the best fuel economy comes with midgrade fuel, premium gives just a tad more pep in hot weather but slightly lower economy.
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Just got it back from my regular mechanic. He agrees with the other mechanics: It is what it is. Having checked out the vacuum lines, O2 sesnor, and computer diagnostics, he could offer no further help.
Too bad! I thought I had a nice car that could be the family campmobile and get decent gas mileage. It just seems odd that a four cyl 2 litre automobile uses 40% more gas than a full-sized chrysler minivan with a 3.3 litre engine (I used to get 28 mpg at 80 miles per hour in the old Grand Caravan that I replaced). To me, however, if the Volvo wagon gets the same mileage as a HUMVEE, I may as well have the room. I didn't buy it for speed, but I guess that is how it was optimized at design.
I am terribly dissapointed. I am just happy that I didn't invest $35K for a new one.
THIS PIG IS FOR SALE!
Dave
This car is going on the market

are
be
not
corners.
letting
gas
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