Are you suspecting mechanical problems, or just looking for general advice? I am not familiar with that car. I get better than advertised MPG with my car.

First of all, how do you measure the MPG? Please don't say you use the gas gauge!

What speed do you drive, what terrain and where are you?

The temperature and road conditions can affect MPG a lot.

If you really want big MPG drive behind a semi or box truck...

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra