It sounds like you have a MAP sensor that is out of range and giving the incorrect signal to the PCM. This will cause poor mileage. When this sensor becomes off a little it will not give a check engine light just poor engine performance.
Here is a diagram to help you get the sensor changed out. Here is what its like on your car (below)
Please let us know what happens.
Cheers, Ken
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Tuesday, September 19th, 2017 AT 1:07 PM