How do i know if the iac valve is bad - 1998 Chevrolet Blazer

most likely the IAC valve is bad , which damaged the ECM also. Have replaced couple of ECMs for this code in 2003 pathfinder. P0507 is an ICS code , which is linked to faulty IAC valve., but the ECM is an issue also, most likely. Find ECM on ebay. and replace the IAC valve with new one.
Wait one minute, your model pathfinder also has giant recall for strut towers rotting out, so have your local dealer check your VIN for the campaign. if the car is rotted beyond repair in certain areas by the struts, Nissan will buy the car back and give you money for it. Check the vin with your local dealer.

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
"I hope this helped you out, if so let me know by pressing the helpful button. Check out some of my other posts if you need more tips and info."
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...

John, IAC normally connected on throttle body, could be on under side. Check the attached links,instruction and guides, Good luck
"I hope this helped you out, if so let me know by pressing the helpful button. Check out some of my other posts if you need more tips and info."
Car Parts Diagram
99 4Runner IAC Cleaning
Symptoms of bad IAC valve

Sounds like a possible idle air control problem (IAC) The smoke probably has nothing to do with the idle problem. Possible valve cover leak??

P1504 Idle Air Control Circuit Malfunction, take off the idle air control and inspect the inside. the pintle inside can get dirty and cause it to get stuck. try cleaning it out with some brake clean and see if it helps. dont spray it ont he electrical connection though.

Get the IAC valve checked.Remove the Iac valve from the throttle body. It is on the side facing the front higher than the tps sensor. It has a 4 wire connector. Make sure this is clean. If it is dirty/dusty then clean it. This valve controls the idle speed. After cleaning it turn the ignition on with the engine off. The Iac should move in and out to find the stops. If it does not move you have either bad wiring, Iac or pcm. Most likely is Iac.
-------- For safety measures,before removing the IAC make sure you don't have any vacuum hoses unplugged. Next make sure the throttle blade closes all the way.Iac is short for idle air control valve. ------- Thanks.Helpmech.

The engine will idle very rough or it will die at idle.

A simple way to test, try removing the IAC valve completely from the intake manifold, leaving an exposed opening to let air in the manifold. If the engine idles ok with the IAC removed, you'll know it's a problem related to the IAC. You will need further testing to determine if the problem is with the IAC valve itself or with its circuit.

Hi there,

Well please follow the below link to check out the position of idle valve -

http://www.freeengineinfo.com/idle-air-control-valve-replacement.htm

The Idle Air Control (IAC) valve controls the engine idle speed and dashpot functions. The valve is located on the side of the throttle body. This valve allows the necessary amount of air, as determined by the Powertrain Control Module (PCM) and controlled by a duty cycle signal, to bypass the throttle plate in order to maintain the proper idle speed.

TESTING
Turn the ignition switch to the OFF position.
Disengage the wiring harness connector from the IAC valve .
Using an ohmmeter, measure the resistance between the terminals of the valve.

NOTE: Due to the diode in the solenoid, place the ohmmeter positive lead on the VPWR terminal and the negative lead on the ISC terminal.
If the resistance is not 7–13 ohms, replace the IAC valve.

The following symptoms can be caused by a faulty IAC due to loose connections, bad grounds, high resistance in the circuit, or opens in the circuit.
 
REMOVAL & INSTALLATION
Disconnect the negative battery cable.
Disengage the wiring harness connector from the IAC valve.
Remove the two retaining screws, then remove the IAC valve and discard the old gasket.

To install:
Clean the IAC valve mounting surface on the throttle body of old gasket material.
Using a new gasket, position the IAC valve on the throttle body. Install and tighten the retaining screws to 71–106 inch lbs. (8–12 Nm).
Attach the wiring harness connector to the IAC valve.
Connect the negative battery cable.


Good Luck!!

Thanks

its located on the throttle body connected to your air intake manifold where your throttle cable connects on the throttle body there is a adjustment screw connected there

Possible base idle adjustment or bad IAC valve. Could also be the A/C circuit. Check to see if the cars idle goes up when you are still and at idle. The idle should come up some, maybe about 150 rpm's or so. If that's OK, that I would have your base idle checked along with the IAC valve circuit and the valve itself. Let me know wht you find.