Ignition Timing/Gas Mileage Question
 

I have an '03 DX, AT, AC with 2.0 (FS engine as opposed to ZM). I've been having an occasional problem with rough idle and poorer than expected mileage. The rated mileage is 25 city/30 highway and I've been getting about 21/27. No check engine light, no codes.

I recently bought a timing light to check the timing. I noticed that at idle, the timing mark seems to jump around a little (about 2 degrees in either direction). Also, if I set the idle to 700 the timing seems to be near specs (10° BTDC), but if I speed the idle up to about 750, the mark hovers aroung TDC. I checked the timing with the car idling in neutral with all electrical loads turned off. When I move the throttle, the timing seems to advance normally.

Is this normal or should I have this checked out at the dealer? I know that the timing is controlled by the PCM and I'm a little worried that something might be wrong, especially when considering the disappointing mileage.

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