Before i replace my iac valve, i want to check for leaks. what is the best, easiest way to do this?

It seems like the problem lies with the engine management system, rather than the brakes. Given that you've already replaced the MAF, MAP, and TPS sensors, here are some other things to check:

1. Vacuum leaks: Inspect all vacuum lines for cracks or damage that may be causing a leak. A vacuum leak can cause erratic idling, poor acceleration, and stalling.

2. Idle air control (IAC) valve: The IAC valve controls the engine's idle speed. A malfunctioning IAC valve can cause the engine to stall during idling. Try cleaning the IAC valve with carburetor cleaner and see if the issue is resolved.

Mark, IAC (Idle Air Control Valve), If engine is idling too fast, problem may not be the idle speed control system, but an engine vacuum leak. Check for vacuum leaks first to rule this possibility out. Also on your Toyota low coolant, air in the cooling system can cause the valve not to operate properly as I believe coolant has to run through valve for it to operate correctly. Fill/bleed air from cooling system. Check the attached links,instruction and guides, Good luck
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Idle Air Control Valve Toyota Nation Forum Toyota Car and Truck Forums
Troubleshoot Idle Speed Control System
Has Anyone Cleaned Their IAC Idle Air Control Valve Toyota Nation Forum...

Vacuum leak , IAC valve - idle air control , Go to your tube an check out videos on checking for vacuum leaks an how to test IAC valve an cleaning throttle plate an IAC - air passages ! Eva codes ? what code # ?

Random multiple cylinder misfire indicates a weak spark or at least that is the most common cause - most misfires are ignition related and as that is the easiest to service and test it is best to eliminate the possibility first.

The coil resistance should be checked against specifications and if found ok test the spark power is sufficient. If the spark is insufficient it is possible it is weak because the ECU is not working correctly or because the voltage supply to the coils is too low. Check the spark plugs for fouling and wear, especially baked on town running deposits.
Clear the code(s) before every test.

P1506 ---Idle Air control (IAC)

IAC Valve--stuck open
Vacuum Leaks- most common cause
Evap System-Leak

Look for Vacuum Leaks
Unplug IAC Valve and listen for change in idle

If you get an idle difference -- remove & try to clean
valve or replace.

Have to get ride of all vacuum leaks first

Not sure on location,but it should be on or near the
throttle body

DTC Description Possible Causes Diagnostic Aides P1504 - Idle Air Control (IAC) Circuit Malfunction This DTC is set when the PCM detects an electrical load failure on the IAC output circuit.

• IAC circuit open
• VPWR to IAC solenoid open
• IAC circuit short to PWR
• IAC circuit short to GND
• Damaged IAC valve
• Damaged PCM

• The IAC solenoid resistance is from 6 to 13 ohms.
  • IAC valve stuck open
  • Vacuum leaks
  • Failed EVAP system
  • Damaged PCM
• The IAC solenoid resistance is from 6 to 13 ohms.

P1507 - Idle Air Control (IAC) Underspeed Error This DTC is set when the PCM detects engine idle speed that is less than the desired rpm.

• IAC circuit open
• IAC circuit short to PWR
• VPWR to IAC solenoid open
• Air inlet is plugged
• Damaged IAC solenoid
• Damaged PCM

• The IAC solenoid resistance is from 6 to 13 ohms
• Disconnect IAC valve and look for no change in engine rpm as an indication of a stuck or damaged valve

P1131 - Lack of HO2S-11 Switch, Sensor Indicates Lean A HEGO sensor indicating lean at the end of a test is trying to correct for an over-rich condition. The test fails when the fuel control system no longer detects switching for a calibrated amount of time.

• Electrical:
  • Short to VPWR in harness or HO2S
  • Water in harness connector
  • Open/Shorted HO2S circuit
  • Corrosion or poor mating terminals and wiring
  • Damaged HO2S
  • Damaged PCM
• Fuel System:
  • Excessive fuel pressure
  • Leaking/contaminated fuel injectors
  • Leaking fuel pressure regulator
  • Low fuel pressure or running out of fuel
  • Vapor recovery system
• Induction System:
  • Air leaks after the MAF
  • Vacuum Leaks
  • PCV system
  • Improperly seated engine oil dipstick
• EGR System:
  • Leaking gasket
  • Stuck EGR valve
  • Leaking diaphragm or EVR
• Base Engine:
  • Oil overfill
  • Cam timing
  • Cylinder compression
  • Exhaust leaks before or near the HO2S(s)

A fuel control HO2S PID switching across 0.45 volt from 0.2 to 0.9 volt indicates a normal switching HO2S.

First look for vacuum leaks on any hose connected to the engine intake manifold. If no leaks, take the idle air control valve off the throttle body and clean the valve, passages, and throttle body with carb cleaner. If you have an ohmmeter, check the resistance on the valve terminals.

1. Visually check the connector, making sure it is connected properly and all of the terminals are straight, tight and free of corrosion.
   
2. Unplug the IAC connector and check resistance between the IAC terminals. Resistance between terminals A to B and terminals C to D should be 40-80 ohms. If resistance is not within specification, the IAC valve must be replaced.

If all is good, replace the valve and test drive. If still having problems, recommend pulling the EGR valve as well and cleaning passages there. Make sure the EGR valve isn't stuck open.




IAC Pinouts:


EGR Valve:

you need to clean your idle air control valve ( or replace it) Spray carb cleaner does a nice job of cleaning it.

This tutorial is from autozone.com

OPERATION

The Idle Air Control (IAC) is a bi-directional motor driven by two coils. The purpose of the IAC valve is to control engine idle speed, while preventing stalls due to changes in the engine load. The IAC valve, mounted in the throttle body, controls bypass air around the throttle plate. The PCM controls engine idle speed by adjusting the position of the IAC motor pintle. The PCM pulses current to the IAC coils in small steps (counts) to extend the pintle into a passage in the throttle body to decrease air flow. The PCM reverses the current pulses to retract the pintle, increasing air flow. This method allows highly accurate control of idle speed and quick response to changes in engine load. If RPM is too low, the PCM will retract the IAC pintle, resulting in more air being bypassed around the throttle plate to increase RPM. If the RPM is too high, the PCM will extend the IAC pintle, allowing less air to be bypassed around the throttle plate, decreasing RPM.

Fig. Typical Idle Air Control (IAC) valve components
During idle, the proper position of the of the IAC pintle is calculated by the PCM based on the battery voltage, coolant temperature, engine load and engine RPM. If the RPM drops below a specified value, and the throttle plate is closed (TP sensor voltage is between 0.20-0.74), the PCM senses a near stall condition. The PCM will then calculate a new IAC pintle position to prevent stalls.
If the IAC valve is disconnected and reconnected with the engine running, the idle RPM will be wrong. In this case, the IAC has to be reset. The IAC resets when the ignition switch is cycled ON and then OFF . When servicing the IAC, it should be disconnected or connected with the ignition switch OFF in order to keep from having to reset the IAC valve.
The position of the IAC pintle affects engine start up and the idle characteristics of the vehicle. If the IAC pintle is fully open, too much air will be allowed into the manifold. This results in high idle speed, along with possible hard starting and a lean air/fuel ratio. A Diagnostic Trouble Code (DTC) may set. If the IAC pintle is stuck closed, too little air will be allowed in the manifold. This results in a low idle speed, along with hard starting and a rich air/fuel ratio. Again, a Diagnostic Trouble Code (DTC) may set. If the IAC pintle is stuck part way open, the idle may be high or low and will not respond to changes in engine load.

TESTING

As with most all engine control sensors used in your vehicle, a thorough and proper test can only be performed by a qualified technician using a scan tool to read the data stream from the PCM. There are a few items a non-professional should check before taking the vehicle to a qualified technician for diagnosis and repair.

Check for a poor connection at the PCM or IAC motor. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connection. Inspect for a damaged wiring harness, especially if heavy work has recently been performed (intake manifold removal, engine removal, etc.) where the throttle body has been disturbed. Inspect for a restricted air intake system. Check for a possible collapsed air intake duct, restricted air filter element or foreign objects blocking the air intake system. Inspect the throttle body. Check for objects blocking the IAC passage or throttle bore. Excessive deposits, especially on high-mileage engines, can build up in the IAC passage and on the IAC pintle. Excessive deposits can also build up on the throttle plate, so check for a sticking throttle plate. Check for vacuum leaks such as disconnected hoses, leaks at the EGR valve and EGR pipe to the intake manifold, leaks at the throttle body, faulty or incorrectly installed PCV valve, leaks at the intake manifold brake booster hose connection, etc.

REMOVAL & INSTALLATION

1. Disconnect the negative battery cable.
2. Detach the electrical connector from the IAC valve.
3. Remove the 2 attaching screws and remove the IAC valve from the engine. Remove the O-ring from the housing.

To install:

Fig. The Idle Air Control (IAC) valve is mounted on the throttle body-3.8L (VIN K) engine shown, others similar

NOTE Before installing a new IAC valve, measure the distance that the valve is extended. The measurement should be made from the motor housing to the end of the valve cone (pintle). The distance should be no greater than 1 1 / 8 inch (28mm). If the pintle is extended too far, adjustment is required, otherwise damage may occur when the IAC valve is installed. Adjust the IAC valve by compressing the pintle to achieve the correct length.

1. Use a new O-ring, install the IAC valve and tighten the retaining screws to 18 inch lbs. (2 Nm).
2. Attach the electrical connector.
3. Connect the negative battery cable.
4. The PCM will reset the IAC valve the next time the ignition switch is turned ON and then OFF .
5. Start the engine and allow to warm to operating temperature to check idle quality.

DTC P1506 is set when the PCM detects the engine idle speed is greater than the desired rpm. This is most commonly caused by a dirty or bad IAC valve. Cleaning the throttle body will, most likely, cure this problem.

p1131 means that the bank #1 O2 sensor, the bank closest to the firewall, cylinders 1-3 is showing a lean mixture. Could be a vacuum leak, a misfire on that bank, an exaust leak upstream of the O2 sensor, fuel control or injector problem on that bank, a faulty O2 sensor, faulty PCM, faulty wiring in the engine control wiring harness.

P0171In the vast majority of cases, simply cleaning the MAF sensor does the trick. 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 also Inspect all vacuum and PCV hoses, replace if necessaryCheck for a dirty fuel filter and proper fuel pressure

This IAC valve runs only when your foot is off the gas pedal. Mainly to keep the engine from stalling and keeping it at a safe RPM. If it is running bad under 2000RPM, more than likely its the IAC valve or a vacuum leak. Clean or replace the IAC valve....Hopefully this helps!!