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Username Post: How do I test an IAC valve        (Topic#270988)
Focus4 
Forum Newbie
Posts: 10

Reg: 09-21-11
10-23-11 08:44 AM - Post#2150236    

I have an 88 5.7 with TBI. I have taken apart the TBI to clean it. Can I somehow verify that the IAC is still good? The connector has 4 pins, is there an ohm test I can perform to verify it is good?



 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3846
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
10-23-11 09:50 AM - Post#2150254    
    In response to Focus4

IAC testing:

Terminals A to B should be 40 to 80 ohms

Terminals C to D should be 40 to 80 ohms

Terminals A to D should be infinite

Terminals B to C should be infinite

I suggest only using a digital (high impedance) ohm meter for doing these tests.


Usually the IAC does not go bad electrically, but it is common for them to stick and stop moving.

The IAC is a stepper motor and uses short pulses of electricity on the wires to move its position.

If the IAC sticks as does not move as it should for each pulse, the IAC count will get off because the computer does not know the actual position of the IAC, but the ECM tracks the commands it has sent to the IAC and assumes it has moved every time it has been sent a pulse.

The IAC units get erratic as they get old and stick. Use care when cleaning the IAC. The IAC should not be cleaned with carburetor cleaner or other harsh chemicals. If the chemicals get down inside the IAC, it will damage it.



For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.


 
Focus4 
Forum Newbie
Posts: 10

Reg: 09-21-11
10-23-11 10:26 AM - Post#2150270    
    In response to Chevytech

Thanks for the info! I checked and the ohm reading's are fine. (50 ohm). Is there way to check for sticking? or just replace it? It is the original. 180k miles.



 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3846
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
10-23-11 05:10 PM - Post#2150418    
    In response to Focus4

There is equipment that will make the IAC move by user command.

The IAC is not a rugged part. It is a common failure.

TPS voltage out of range, and other problems, can cause the ECM to send no pulses to the IAC.


For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.


 
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