Engine Performance problem
1991 Toyota Corolla 4 cyl Two Wheel Drive Manual 170060 miles
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I have a 1991 Toyota corolla (170060 mileage)that is using a tank of gasoline in a week. Before this problem started it gave me three week for a tank.

I have replace the fuel pump, fuel filter, clean the fuel injectors and changed the distributor and spark plugs. What can be causing this problem for low gas mileage?

Most likely a bad sensor e.g. coolant temp, O2 etc.

It is also possible the CAT is clogged. Best thing to do is to have the ECM scanned to make sure all the sensors are in proper range.

You should be seeing black smoke out the exhaust indicating a rich mixture.
You should also have a check engine light?

One other thing is that running the AC on a car can reduce fuel mileage significantly, because it takes more power to run the compressor.