Poor fuel economy and loss of power

A week ago my 1995 Toyota Corolla’s check engine light turned on. From that point on, I’ve noticed poor fuel economy (usually get 30 MPG, now get 23 MPG) and a significant loss of power especially when going up hill. The car idles rough at neutral. The engine hesitates when the car reaches 30 MPH and again at 50 MPH. Could my problem be one of the following? 1. a bad mass air flow sensor, 2. a bad oxygen sensor, 3. need of a tune up (last one done August 2009) Any ideas would be greatly appreciated. Thanks. Mike Jorge

It is very possible that a bad oxygen sensor is the problem, but it could be any one of a myriad of other possibilities also.

Why guess?
Have the stored trouble code(s) read, come back to this forum to post them, and then we can discuss things more concretely.

It could be #1, or #2, or a bad coil(s), or lots of other things. Assume the spark plugs were replaced during the “tune up” then the plugs are likely OK. The rest of a “tune up” is up to the shop doing it but usually new plugs are involved in a tune up.

Go to an AutoZone or other parts store and get the codes stored in the cars computer read and post the #'s that came up on the scan.