Mighty Max, Poor mpg

I have a 1991 Mitsubishi Mighty Max (engine 2.4, fuel injection) . I had the timing belt changed at 59,000 miles a couple of months ago, my gas mileaged dropped from 18 mpg to 10 mpg.
Shortly after the engine light appeared. I was told the mass air flow was bad so we replaced it. The vehicle started to burn very rich and leaving carbon deposits on the plugs so, we changed the 02 sensor, heat sensor, plugs, wires, cap, rotor and fuel filter. NO carbon build up on plugs. But, Failed EMISSION TEST, both high and low "C0"

Had the injectors cleaned, barely passed EMISSIONs.

NOW: Ater driving for 300 miles since inspection, I am still getting 10 mpg, and now getting carbon build up on the plugs.

When I first start the engine, I need to idle around 1700 rpm due to very rough idle, after about 1.5 minutes the engine will idle smoothly, but the engine seems to be burning rich and when I revvvvv the engine in PARK, the engine starts to bog down at the higher RPMs.


I also, replaced 2 sets of plugs, up to ranges.


Any suggestions would be appreciated. I have spent $900 for labor and parts, and my Mighty Max runs worse than ever.