P0171 is system too lean bank 1, P0174 is too lean bank 2, and 302 is misfire bank 1. Look for vacuum leaks. If you don't find them, put a vacuum gage on it can check. The P0171 is almost always a vacuum leak. If not other possibilities are front O2 sensor is too old and should be replaced (if mileage is greater than 100k then replace). Try injector cleaner. Misfires are usually bad spark plugs, but could possibly be caused by insufficient fuel. I've never had a car of mine in bad enough shape to have that error.
P0171=THROTTLE MOTOR POSTION 2, RANGE/PERFORMANCE PROBLEM.. P0174= FUEL MEARSUREMENT SYSTEM BANK 1, INJECTION TIMING INCORRECT....P0302 RANDOM/ MUTLIPLE MISSFIRE DETECTED ???
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