2001 toyota celica vaccum leak, po171 keeps comingon

Hi Chris.

p0304 = Number 4 Cylinder Misfire Detected

Faulty spark plug 4
Clogged or faulty fuel injector 4
Faulty ignition coil 4
Fuel injector 4 harness is open or shorted
Fuel injector 4 circuit poor electrical connection
Ignition coil 4 harness is open or shorted
Ignition coil 4 circuit poor electrical connection
Insufficient cylinder 4 compression
Incorrect fuel pressure
Intake air leak

The P0304 code means that the cylinder 4 is misfiring or is randomly misfiring. Start by checking for intake leaks an if no leaks are found the next step is to replace the spark plugs on cylinder 4.


p0102 = Mass or Volume Air Flow Circuit Low Input

Faulty mass air flow sensor
Intake air leaks
Dirty mass air flow sensor
Dirty mass air filter
Mass air flow sensor harness is open or shorted
Mass air flow sensor circuit poor electrical connection

Before replacing the mass air flow sensor, try replacing the air filter and cleaning the air flow sensor with low compress air or mass air flow sensor cleaner.
Reset code and drive vehicle.
If the code comes back, it may be necessary to replaced the mass air flow sensor.


p0154 = O2 Sensor Circuit No Activity Detected Sensor 1 Bank 2

Faulty Front Heated Oxygen Sensor Bank 2
Front Heated Oxygen Sensor Bank 2 harness is open or shorted
Front Heated Oxygen Sensor Bank 2 circuit poor electrical connection
Inappropriate fuel pressure
Faulty fuel injectors
Intake air leaks may be faulty
Exhaust gas leaks

Replacing the Front Heated Oxygen Sensor Bank 2 usually takes care of the problem.


p0113 = Intake Air Temperature Sensor Circuit High

Faulty Intake Air Temperature (IAT) sensor
Dirty air filter
Intake Air Temperature (IAT) sensor harness is open or shorted
Intake Air Temperature (IAT) sensor circuit poor electrical connection

The Intake Air Temperature (IAT) sensor is built into mass air flow sensor or in some vehicles mounted to the air filter duct housing. The sensor detects intake air temperature and transmits a signal to the Engine Control Module (ECM).The temperature sensing unit uses a thermistor which is sensitive to the change in temperature. Electrical resistance of the thermistor decreases in response to the temperature rise. The Intake Air Temperature signal is used as an input for various systems in the vehicle.



Hope this helps
FYT

http://www.autocodes.com/make/nissan

Check for intake leaks, intake hose leaks, check mass air flow sensor.
02 sensors will keep setting off a lean code until the air problem is fixed.

Almost always caused by a vacuum leak, look for a damaged hose, or one that has become disconnected. It can also be caused by a leaking intake gasket or a leaking exhaust manifold before the O2 sensor.

THE MASS AIR FLOW SENSOR IS MOUNTED TO THE INTAKE AIR HOSE OF THE AIR CLEANER ASSEMBLY. O2 SENSORS LOCATION.YOU HAVE 2 # O2 SENSORS.YOU HAVE ONE THE EXHAUST MANIFOLD.THE OTHER SENSOR LOCATED DOWN AT THE CATALYTIC CONVERTER. YOU SHOULD ALSO REPLACE THE O2 SENSORS TO HAVE THE BEST READINGS FOR AIR MIX.

Either the mass-air sensor is bad, which normally throws a mass-air voltage code, or you definitely have an air leak post the mass-air. Smoke the intake manifold with a smoke machine or spray the whole intake to head, including to brake booster with brake cleaner and listen for a change in idle. Focus on the gasket surface of the intake manifold.

PO171-System to Lean (Bank 1)

Air filter cover tight?
All intake ducting tight?
Clean MAF Sensor.--CRC MAF Cleaner
Fuel Pressure Regulator?
EVAP Purge Valve-stuck open?
Vacuum leaks?
EGR System-issues?

Seems your getting a lean O2 Code,because it is trying to correct for a rich condition,as you said.

Is the Throttle Position Sensor-original?

Work on what is driving it rich,my list is a possible.

Hi Jonah,

I have the same problem and it only propped up after i had my exhaust manifold repaired, do you think the mechanic didnt do the weld it right?

James
2001 Saturn L200

You might try plugs, wires, fuel filter, air filter & PVC valve..

there are two reasons why this code will set 1st is a vaccum leak next is a bad mass air flow sensor if you have access to a good diagnostic computer you can read live data to pinpoint the problem if you don't have access try to find the vaccum leak in the engine compartment if there isn't one replace the mass air flow sensor

Yup! I know exactly what it is.. Intake is leaking .. ( pssst ) its plastic