May seem obvious, but check your odometer. Could be sticking, slipping, or wrong based on tire size.

I fixed my ODO last year, so I can track MPG now. Almost all city driving, mostly below 40, pretty consistent between 23 and 26 MPG, at 5280 feet altitude. Auto trans.

Highway at 55 to 65, have gotten up to 28. Higher speeds start decreasing MPG. I have never been in the 30's, no matter what.

These cars were built when the national speed limit was 55, so that makes a difference as well. EPA MPG when new was something like 24 -33. I am sure the 33 was a manual trans, running right a 55, on a very flat track.......

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2002 E320 Sedan 93K Designo Mocha Black Metallic!
1995 E320 Wagon 205K Black Wagon
1982 240D 183K SloPoke

I believe each of these cars are the final production year for that model.