My 2001 toy,corolla showed a code of po171 so i changed the oxygen sensor then showed po300 , the car hesitate on excelleration but if you back up a little on the throttle it runs fine like the cat is pluged so i seperated the cat at the exost mount didn't change a thing any ideas

all misfires and bad mixture of fuel and air

https://www.google.com/search?q=05+TAURUS+CODE+SHOWING+po171+po174+po300+pO303+pO304

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codes p 0014, 0340, 0341, 0345, 0346 all refer to the cam shaft position sensor==causes include-- advance mechanism faulty - CMP sensor --insecure cam rotor --wiring short to ground --air gap--ECM
codes p 0420, 0431 refer to the cat converter=== causes --cat converter failed ---wiring --- HO2S ( heated oxygen sensor)
code p 171 is a faulty HO2S sensor and
p 174 refers to system too lean bank 2===causes --intake /exhaust leak---fuel pressure /pump---injectorr/s AIR system---hose connection/s

P0171 =system too lean (bank 1)
P0300 = multiple misfire
P0463 = fuel level sensor circuit high input
P0480 = cooling fan 1 control circuit

PO171 OBD2 Code basically this means that an oxygen sensor in bank 1 has detected a lean condition (too much oxygen in the exhaust). On V6/V8/V10 engines, Bank 1 is the side of the engine that has cylinder #1. The P0171 is one of the more common trouble codes.

his code is triggered by the first downstream (front) O2 sensor. The sensor provides a reading of the air:fuel ratio leaving the engine's cylinders, and the vehicles powertrain/engine control module (PCM/ECM) uses that reading and adjusts to keep the engine running at that optimum ratio of 14.7:1. If something is not right and the PCM cannot maintain the 14.7:1 ratio, but rather there is too much air, it triggers this code.

the po300 code is for a cylinder misfire, usually followed by a last number of 1 2 3 ect, showing which cylinder is misfiring, normally this can be fixed by installing a new set of plugs, the po171 code could be this

• 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. you cleaned that but it could be fouling out you could also have this happening
• • Inspect all vacuum and PCV hoses, replace if necessary
  • Check for a dirty fuel filter and proper fuel pressure

The P0172 code is a rich code most likely caused by the P0300. The P0300 is a random/multiple cylinder misfire code. Replace the plugs and wires.

po171 is lean on bank 1--===causes --MAF/VAF sensors --injectors ---HO2S (heated oxygen sensor)
po300 is random misfires and po301, 2, 3 4 5 6 etc is the cylinder that is misfiring
most likely that the fuel pressure is below the required pressure either from the pump or blocked filter or the tank not venting properly--- (EVAP) problem
check the fuel pressure ( minimum of 45-65psi) --problem pressure regulator , pump or filter
replace the heated oxygen sensor on bank 1 ( in the exhaust manifold before the cat converter) as it reports to the ECM to get the correct air/fuel mix

po328 is your knock sensor the po300-304 is your cranksensor change that and most problems will go away remember to disconnect the battery
the knocksensor can still play a roll if the car doesn't want to start each one of thors sensors are at autozone 40.00 bucks to 60:00 covers it

you need to change the oxygen sensor. it will soon cause you problems. after you need to take it in to  erase the code.

Basically this means that an oxygen sensor in bank 1 detected a lean condition (too much oxygen in the exhaust).