C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

IACV Data

Old Mar 13, 2018 | 02:54 PM
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Default IACV Data

So I got my Tuner Pro working and had IACV data on the screen. I picked a few values at random just to test the connection and see if data was flowing.

What was it telling me?

At start up (Ambient temp 55F), steps read 44. Value dropped as the engine warmed. Eventually read 0. Went up to around 9 or 10 if I pressed on the accelerator. Then would come back to zero when I let off.

IACV minimum steps always read 10.
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Old Mar 14, 2018 | 11:25 AM
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Originally Posted by belairbrian
At start up (Ambient temp 55F), steps read 44.

Value dropped as the engine warmed.

Eventually read 0. Went up to around 9 or 10 if I pressed on the accelerator. Then would come back to zero when I let off.

IACV minimum steps always read 10.
Doesn't tell me too much there.

It should

I would shoot for 20-30 counts just to give it some "space" to back down to for whatever reason. I think if it is 0 counts, you need to do some work. Assuming everything is off but the motor, I would turn the adjustment screw out. This closes the blades and forces the ECM to use the IAC. Rev and check what it settles down to. If it is still 0, turn it out some more. Rev and recheck. If you turn the screw all the way out and it still is 0, it makes me think you have an air leak. One that got worse as the motor got hot. After that I would adjust the TPS.

Another thing I wonder about is how clean is the TB? Would you be able to take it off, take the IAC solenoid off and the IAC housing and the top plate? That would make cleaning the passages easier.

I would NOT push or pull the IAC solenoid pintle or bad things could happen. Ask me how I know. I'd use brake cleaner. Spray it GENTLY and wipe the pintle GENTLY with soft tissue till it comes clean. Rest of the IAC you can hose down with the brake cleaner. Obviously, new gaskets needed for reinstall so don't start till you have them.
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Old Mar 14, 2018 | 07:19 PM
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The throttle body and IACV were cleaned a few months ago when i had it off doing the opti. All new gaskets at that time.

After reading your response a light kind of clicked on in my mind.

If the IACV was really at 0 steps it would be closed so no air to engine. Since the engine is idling it's getting air either through the IAC path or an an air leak. I checked and the throttle plates are closed and against the stop.
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Old Mar 14, 2018 | 08:56 PM
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Originally Posted by belairbrian
The throttle body and IACV were cleaned a few months ago when i had it off doing the opti. All new gaskets at that time.

After reading your response a light kind of clicked on in my mind.

If the IACV was really at 0 steps it would be closed so no air to engine. Since the engine is idling it's getting air either through the IAC path or an an air leak. I checked and the throttle plates are closed and against the stop.
That is what I would think but is your screw all the way out? If so you need to find out where you are leaking from. Start with your hoses on the Manifold. Pull one out, plug it and rebuild and check Once you find the one that makes the IAC counter go up and stay up, your leak is in that circuit

If you cannot find it check out the gaskets on the manifold. I have had that problem with the manifold to runners gasket.
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Old Mar 15, 2018 | 05:54 AM
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Originally Posted by belairbrian
The throttle body and IACV were cleaned a few months ago when i had it off doing the opti. All new gaskets at that time.

After reading your response a light kind of clicked on in my mind.

If the IACV was really at 0 steps it would be closed so no air to engine. Since the engine is idling it's getting air either through the IAC path or an an air leak. I checked and the throttle plates are closed and against the stop.
You may have an air leak but my guess is the throttle stop screw is holding the throttle blades open slighrly. Check the basics and if all is well reset the idle stop screw to give a warm idle no load iac count of 10 ish.
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