IACV issue?

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11-06-2018, 06:47 PM

Slader Roberts

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IACV issue?

Hey guys new to the forums. Just bought a truck here in Austin TX. 2001 Chevy, Single Cab, 4.8 vortec, Manual transmission, Stepside. Great clean truck. One issue so far is the truck will hold rpms when letting off the throttle in gear... and sometimes free revving it will stick and rev up to 3,000 rpm on its own and hold for 4 to 5 seconds then slowly drop to idle. I checked the TB and IACV. Replaced the IACV and the truck ran MUCH worse(stalling, holding rpms) so I put the old one back in. Is there a teach in process for a new IACV? Really would like to drive the truck with rpms not sticking on decel. TB cable is also fine.

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11-06-2018, 08:59 PM

Jutsumguy

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Have u checked the tps

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11-06-2018, 09:08 PM

Slader Roberts

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I checked operation with a scan tool just 0% to 100% pedal travel.

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11-07-2018, 05:15 PM

PFIX

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You can do a relearn by disconnecting the negative battery cable. Reconnect the cable and with the engine at normal operating temperature let engine idle for 5 min. Turn off the key and restart.
Also check to ensure your throttle is closing all the way onto the throttle stop at all temps. Your TPS should be reading about .5 volts when at closed throttle. This should be a yellow wire at the TPS connector that is the output signal to ECM.
Do you have an aftermarket throttle body or stock? Are there any faults stored in the ECM?

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11-07-2018, 05:42 PM

Slader Roberts

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Thank you!! It is the stock throttle body.

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11-20-2018, 10:28 AM

axekick

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Do you know if it's ever been tuned?

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11-20-2018, 03:50 PM

Last Call

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I've had bad luck with new but aftermarket IAC valves. I only use AC Delco, and never had an issue. A few ideas:

Reset the TPS, disconnect [plug at TPS sensor, ignition on for 15 seconds, off, then reconnect. That should zero out the TPS percentage reading in the PCM.

It would not be a bad idea to check for a vacuum leak somewhere.

And it would be good to see if the PCM has been tuned, that can also be the culprit.

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11-20-2018, 06:13 PM

RedXray

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Quote:

Originally Posted by Last Call

And it would be good to see if the PCM has been tuned, that can also be the culprit.

If it's the "cracker" settings in HP Tuners... when you push in the clutch the idle will hang at like somewhere around 1200 to 1500 until you come to a complete stop, then the engine drops to the commanded idle set in the tune. That can be tweaked in the cracker settings (but 3000 rpm it's probably something else). Just something to look at after any relearn and sensor replacements fails to work. It could also be a worn or damaged throttle body itself causing the throttle blade to stick on the housing. If all fails just replace the TB with a used one from the J/Y.

I found a new (New Old Stock) ACDelco on ebay with sensors, still in the beat up box, for my truck, $75 shipped