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The p0171 is usually going to be a bad o2 sensor relating to the heater circuit, however the p0141 is related to system running too lean: http://www.obd-codes.com/p0171
A code P0171 may mean that one or more of the following has happened: The MAF (Mass Air Flow) Sensor is dirty or faulty Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry. There could be a vacuum leak downstream of the MAF sensor Possible cracked vacuum or PCV line/connection Faulty or stuck open PCV valve Failed or faulty oxygen sensor (bank 1, sensor 1) Sticking/plugged or failed fuel injector Low fuel pressure (possible plugged/dirty fuel filter!) Exhaust leak between engine and first oxygen sensor.
I would also check your timing and the valves in the head seeing that the head had work done and could likely be related.
Check fuel pressure as well via a fuel pressure tester and use of professional scan tool will greatly help you with diagnosis as being able to watch systems on the same screen. Checking maf etc.
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