2001 Toyota corolla hesitates on acceleration

Disconnect the maf and see if it starts, if not the MAF is not the problem.

sounds like a faulty fuel pressure regulator, i checked out code P0171 and that is correct.
good luck,
frank

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

P0171 - System Too Lean (Bank 1)
Basically this means that an oxygen sensor in bank 1 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.

Note: This DTC is very similar to P0174, and in fact your vehicle may show both codes at the same time.

Symptoms: You will more than likely not notice any drivability problems, although there may be symptoms such as a lack of power, detonation (spark knock), and/or a hesitation/surge on acceleration.

Causes: 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 solutions include:
* In the vast majority of cases, simply cleaning the MAF sensor does the trick. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
* Inspect all vacuum and PCV hoses, replace if necessary
* Check for a dirty fuel filter and proper fuel pressure


Hope this helps (remember to rate this answer).

Did you erase the fault codes from the ecu computer, with the scanner, after the repairs were performed?

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

p0171 is lean condition bank one. you could have a vacuum leak a bad map sensor bad maf sensor clogged fuel filter low fuel pressure. start with the vacuum leak first.

Clean the MAF sensor with CRC brans MAF spray cleaner.

No need to replace the MAF. If it was bad, the check engine light would have come right back on as soon as you started the engine. The MAF not only measures the air going into the engine, but also measures the air temperature. Those 2 circuits are constantly sending info the the ECU. If either would fail, the ECU would light the check engine light. P0171 is a common code for incorrect readings (dirty) in the MAF. Cleaning it always helps, and cuts off the light. Your acceleration problem may be either a wrong Air-Fuel sensor (the one before the cat), or an "aftermarket" AF sensor. "Aftermarket" AF sensors have been shown to not work properly in Toyota vehicles. Hope this helps

If you had a bad MAF, the check engine light would have come on instantly. Replacing the MAF will NOT cure your issue. P-0171 is a common code, and cleaning it always eliminates the P-0171. Regarding the sensor, there are 2 different ones, and they do NOT interchange. If your body shop put in an "aftermarket" air-fuel sensor (the one closest to the engine), you can expect hesitation issues.