Other than a vacuum leak why would IAC drift down to 0

94 LT1 on run stand with Long Tube Open Headers. No emissions are on the engine and have been tuned out. Basically a naked engine with an alternator. The engine idles and revs up well but I noticed the IAC counts drift to 0 after a few minutes of running in closed loop. I checked somethings that I thought might be leaking and sealed a grommet where the air intake temp sensor goes in. I thought that might affect the MAF reading which also blink red (low). I did not find any vacuum leaks visually or with a tank of propane moved all over the intake.

I was wondering what other than a leak will cause IAC counts to go to 0? And, does it matter?

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I was wondering what other than a leak will cause IAC counts to go to 0?

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it's trying to hit a 600 rpm target and can't get lower than ~700, that's why it's hitting zero.

other than a vacuum leak, throttle plates that are too far open will do it.

your idle target is pretty low, though, and it seems to think it's in gear, is the transmission actually connected and providing load, or is it just a flywheel?

it might just be trying to hit an in-gear idle target and not being able to go that low without that load.

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And, does it matter?

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yeah it does, the IAC is feeding the idle passages in the plenum, you want all your air going through those passages, and pretty much none through your throttle plates, you should never see zero counts on an LT1

Thanks, Steveo. It just has the flywheel/flexplate on it. I don't know why it thinks it's in gear unless it's because the bin says it is an automatic but one isn't plugged in. Could be a harness issue too as I stripped down the original harness to make it stand alone and might have missed something. (but I think I didn't miss anything) I might switch the bin to a stick transmission if that will eliminate that issue.

There is no block off plug on the throttle plate adjustment so maybe they are open a tiny bit. I have thoroughly cleaned the throttle body so no junk is holding them open. The idle target is what the 16210011 calibration came with.

My grandson rebuilds transmissions so I guess I need to get one built up and put it behind the engine.

I said I wasn't going to ask more questions since the engine on a stand is not a normal situation and provides no real load data. Nevertheless, I did and you answered it so I appreciate it. I learn something every time.