Is this a bad IAC valve, 95 Buick 3100 V6?

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Apr 27, 2010
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Engine idles at 1200-1300 rpm in park when warm. Connected scan tool and the desired idle says 800. Go to the IAC ouput section and manually drop the idle down in 25 rpm increments to 550 rpm but the engine stays at 1200. Next I manually raise the idle speed to about 1600 rpm in 25 rpm increments, and once the tool commands 1200 and higher speeds, the idle does increase and follow the commands. Stop at 1600 at which point I try to drop the idle, but it stays at 1600. If I shut the engine off and turn it back on, it's at 1200 again with the tool commanding 800 rpm. Is this a IAC problem? Like the valve is sticking open. Can it be tested on the bench or cleaned?
 
It certainly seems like sticky valve right? But why does it drop back down after the shutoff? I would check the MAF values to see if it behaves like described operation and output specs. Simple thing thats cheap is to clean it with MAF cleaner ONLY. Test functions after that, hopefully that'll help some.
You can take out the IAC and see if there's carbon build up in the valve or the passages on the throttle body. If its all plugged up with carbon, manually operate the valve and see if its sticking open. Clean it with solvents like brake cleaner or intake cleaner (I use non-chlorinated brake cleaner) and check free movement of valve to see if its still sticky. I'd reinstall making sure the gasket was ok, and test its function again.. Hopefully it helps with the idle issue. If its better but not perfect, I'd just change it with an OE valve if the cost isn't too high.

I'm not sure about GM's sensor functions that effect the PCMs adjustments on air/fuel rations, when the mixtures are adjusted to facilitate warm up, or in closed loop when the O2 sensor is in closed loop.

I'm not personally intimate with bench testing the valve with a meter, I'm sure there's something on you tube.

Wait, are you testing the car when its cold or when its warmed up?
 
Took the valve out and no significant carbon build up but cleaned it and the passage anyway. Throttle body cleaned recently. Commanded the valve position with the scan tool and the pintle extended and flew out. Took 5 minutes to find it. Not sure it's supposed to do that. Says made in Mexico but no other markings. New one is fairly cheap so I'll replace it.
 
Yeah they don't stop easily when power is supplied, made that mistake as well. Could also be TPS, vacuum leak or worse case the lower intake manifold leaking causing a vacuum leak. I would disconnect the battery and have the ecu do an idle relearn when you get the new one installed and see if that helps.
 
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