2001 Tacoma running rich but the scanner is reading a lean code

P0102 - Mass Air Flow Sensor Circuit Malfunction

The mass air flow or MAF sensor is placed in the intake air duct between the air filter and the engine intake manifold. The MAF sensor measures the amount of intake air flow. The MAF sensor converts the air flow measurement into a voltage or frequency signal, with the voltage or frequency changing proportionally to the amount of air flow. The air flow sensor signal is monitored by the engine computer (ECM). The engine computer (ECM) uses the mass air flow signal to know the engine load and to calculate the proper amount of fuel injected. If the signal from the mass air flow sensor is out of expected range, the ECM detects a fault and sets the code P0100. For example, the mass air flow sensor signal could be higher than expected when the engine is not running or lower than expected with the engine running. A car with the code P0100 may have some driveability issues, such as stalling, lack of power, surging, hesitation, etc. In some cars, the code P0100 can cause the fail-safe mode where the engine speed would be limited to 2,500 - 3,000 rpm.
If there are other trouble codes present, they might need to be looked at first. Checking the freeze frame may help, as it may contain some important information. The freeze frame is a snapshot of the engine parameters at the moment when the fault was detected. The freeze-frame may show whether the vehicle was running or stopped, whether the air-fuel ratio was lean or rich, was the engine was cold or warmed up at the time of the malfunction. Read more about the freeze frame.

Read more about mass air flow sensor.

What could cause the code P0100:
- faulty or contaminated mass air flow sensor
- open or short in the mass air flow sensor electrical circuit
- open or short in the sensor power or ground circuit

- other electrical problem with the MAF sensor wiring, (corroded wires, bent terminals, bad ground connection, burned fuse, etc.
- vacuum leaks
- restricted air flow at or before the air filter
- wrong air flow sensor installed
- problem with ECM

P0102 - Mass Air Flow Sensor Circuit Low

The mass air flow or MAF sensor measures the amount of air entering the engine. The engine computer (ECM) uses the mass air flow signal to calculate the amount of fuel injected (read more how the MAF sensor works below). The code P0102 is set when the signal from the mass air flow sensor is lower than expected. Often a car may exhibit some driveability symptoms, such as lack of power, surging, hesitation on acceleration, hard starting, pinging (detonation), or rough idle when started cold. Often the codes P0171 or P0174 could also be stored along with the code P0102, as the incorrect air flow signal can cause the engine to run lean. The codes P0171 and P0174 indicate a lean condition. Checking the freeze frame might help in the diagnostic process. The freeze frame is stored in the ECM along with the trouble code. The freeze frame contains some recorded parameters (e.g. vehicle speed, engine temperature, fuel trim) at the moment when the fault was detected. The freeze frame can also be accessed with a scan tool.

What could cause the code P0102
- faulty or contaminated mass airflow sensor
- debris blocking the air flow at the mass air flow sensor
- unmetered air leaking past the MAF sensor (vacuum leaks)
- PCV system vacuum leaks
- restricted or collapsed intake air duct
- dirty or restricted air filter
- restricted air screen before the air filter
- improper application of aftermarket components (e.g. cold intake, modified air filter, etc.)
- wrong air flow sensor installed
- electrical problem with the MAF sensor wiring, connector, power supply or ground.
- problem with ECM
- in some cases other issues with the fuel injection system like a clogged catalytic converter or a faulty manifold absolute pressure sensor (MAP) can also cause the code P0102.

Solution for MAF repair

Did you mean the mass air flow sensor ! hear are some problems that accure. So, MAF failure will create a wide variety of performance and power problems. These may include: hard to start vehicle; starts and immediately stalls; hesitation in engine; rough idle; running very rich or very lean fuel mixture; or "hiccup" when accelerating.
If you suspect MAF sensor failure and the check engine light is on, a auto parts store can read the computer code for free as long as light is on with a code scanner or even sell you a code scanner. An auto repair shop can also check the codes fairly easily. But if the check engine light is not on and you suspect MAF failure, try the cleaning the maf sensor first. good-day !.

P1137 is HO2S Bank 1 Sensor 2 Lean Or Low Voltage. Oxygen sensor is reading a "lean condition". This code probably is stored from the rough and low idling. So it sounds like you maybe having other issues causing this P1137 code to come up. For lean conditions read this:
1. Vacuum leaks - check for failed or loose vacuum lines, leaking intake gaskets, intake air tubes loose or any other source of un-metered air leaks (leaks after the Mass Air Flow Sensor)
2. Restricted fuel filter or bent/pinched fuel system lines
3. Incorrect input from other sensors, such as the Mass Air Flow Sensor/cam or crank sensors, which may not always drop a separate code
4. Engine misfire ? Yes I know this one may seem weird. You might think that if there is a misfire then you will have all that unburned fuel and it should read rich; right? Well the O2 sensors read only oxygen content in the exhaust, so if you have all that unburned fuel from incomplete combustion then, you guessed it, you also have all that unburned oxygen. High O2 content in exhaust equals a lean reading!

P0174 Generic Definition

Fuel Trim Bank Two Condition
- The ECM has detected a rich or lean air/fuel ratio condition on engine bank two

Probable Cause[s]

1. If bank one and two are set together suspect a fuel pressure condition or MAF sensor fault
2. Failed HO2S21
3. Ignition misfire condition
4. Fuel injector problem
5. Engine mechanical condition

P0171 Generic Definition

Fuel trim bank one condition
- The powertrain control module uses the oxygen sensor to calculate the air/fuel ratio of the engine. The computer has recognized a rich or lean condition on one engine bank only.

Probable Cause[s]

1. If bank one and two codes set together suspect fuel pressure or MAF (Mass Air Flow) Sensor
2. Oxygen sensor defective
3. Ignition misfire-repair
4. Fuel injector problem

ok heres problem 101 is mass air flow sensor 171 running too rich 174 running too lean can find 429 but it the same lines i believe take out your mass air flow sensor and clean it check it connection if comes back on replace the mass air flow sensor

what should we check when we have those pesky rich or lean codes? The most common issues for lean codes are:

1. Vacuum leaks - check for failed or loose vacuum lines, leaking intake gaskets, intake air tubes loose or any other source of un-metered air leaks (leaks after the Mass Air Flow Sensor)
2. Restricted fuel filter or bent/pinched fuel system lines
3. Incorrect input from other sensors, such as the Mass Air Flow Sensor, which may not always drop a separate code
4. Engine misfire – Yes I know this one may seem weird. You might think that if there is a misfire then you will have all that unburned fuel and it should read rich; right? Well the O2 sensors read only oxygen content in the exhaust, so if you have all that unburned fuel from incomplete combustion then, you guessed it, you also have all that unburned oxygen. High O2 content in exhaust equals a lean reading! There are also some other possibilities such as an internally leaking EGR system, (but this will typically set a separate code). A leak in the exhaust system before the O2 sensor will also cause incorrect readings. And always check for after- market modifications. These can throw a wrench into the works! The only other possibilities (however unlikely), are wiring issues, computer concerns or a bad O2 sensor! .

Take it to Advance Auto or Autozone and they'll read the check engine code. That will give you an idea but it's not perfect. There are many faults that trip the check engine light and I suspect there will be several. Coils or Mass Air Flow sensor would be at the top of my list of suspects. A bS Mass Air Flow sensor will give other codes such as lean or rich or even manifold leak, because the result is the fuel system doesn't provide proper ratio of fuel to air.

those codes tell me your system is running rich and mutiple missfires. So I suspect it's your mass air flow sensor. It's located on the duct work from your air cleaner box to the throttle body. NOTE! A crack duct could also be causing this problem. Air can be escaping through this duct making the reading the flow sensor took to be incorrect.

those codes are for lean engine condition look for vac leaks at the back of engine to the pcv valve could hear hissing noise with engine running also check egr valve to be stuck open also when was last fuel filter changed? hope this helps .

It might but what exactly are the codes. Before you change the Mass air flow sensor, try cleaning it first with a can of mass flow cleaner.
If your running a oil K&N filter, there could be some oil residue on the sensor. Start with that and change the filter or clean it if it's a K&N.
The O2 sensor's could be bad also, you really need the code's to be sure what sensor is giving you the faulty signal.
Good luck and hope this helps.