My check engine light went on & will not turn off. on 1999 Toyota RAV4

Took to shop & changed EGR valve but it came back on. Had friend code it & got P1133, P0401 & P0171. How can I fix?

Asked by for the 1999 Toyota RAV4
An EGR valve is used to enrich the fuel mixture, by introducing exhaust gas back into the intake. The LEAN code shows you're not getting enough fuel for a proper mixture. Possible causes are Vacuum leak, Fuel filter restriction, weak Fuel Pump, o2 sensor, or maybe a Mass Air Flow sensor. Run fuel data on scan tool for short term fuel,o2 sensor data. Maybe need to take it to a repair facility who knows what to look for. This same problem happens quite often on most vehicles.
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sad to say, but i had this problem with my 2008. had oil change, new filter. all fluids checked. just regular routine maintanence . my light went out. didn't run diagnostics. not sure if this is your problem, but read my manual it states your engine light will come on when oil change, fluids checked is due.
Replace the Manifold Absolute Pressure sensor. The coolant code may not disappear though, as long you're not overheating, hey. I had all the very same codes come up in mine and the egr is the last on the list for repair. Also, new spark plug wires may help, bad wires can trigger the false o2 reading you got, that was where mine came from. Good luck! Also, our ravs don't have mass air flow, they have the Manifold Absolute Pressure sensor.
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