Need Help with idle
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Teching In
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Need Help with idle 5.3 swapped Nissan 350z with a Texas speed cam fully tuned on a 02 Silverado PCM
the throttle body has been replaced 3 times as well as a new gm tps and iac.
car warm I reset the TPs and iac unplugged both key on then off plugged back in and key off.
idles at either 900 or 650 when at a stop.
stalled the car idles jumped to 1500 wouldn’t go back down until I stopped unplugged the TPs and iac key off and key on the went back to 650 or 900.
Drove another 20 miles idles at either those two values.
stalled again pulling into my garage.
car now idles at 1500 again.
im having trouble figuring out why the car won’t just keep an idle value and it either freaks out or just doesn’t have a consistent set idle.
tuner has idle set at 850.
A/F is good all gm parts with sniper holly throttle body cable driven.
looking for answers because I am out of ideas.
the throttle body has been replaced 3 times as well as a new gm tps and iac.
car warm I reset the TPs and iac unplugged both key on then off plugged back in and key off.
idles at either 900 or 650 when at a stop.
stalled the car idles jumped to 1500 wouldn’t go back down until I stopped unplugged the TPs and iac key off and key on the went back to 650 or 900.
Drove another 20 miles idles at either those two values.
stalled again pulling into my garage.
car now idles at 1500 again.
im having trouble figuring out why the car won’t just keep an idle value and it either freaks out or just doesn’t have a consistent set idle.
tuner has idle set at 850.
A/F is good all gm parts with sniper holly throttle body cable driven.
looking for answers because I am out of ideas.
Last edited by Che70velle; Nov 30, 2025 at 08:14 PM.
Your text was printed in gray color…I fixed it.
So I had a similiar issue…albeit not as yours…with a 6 liter build and a Holley TB. The IAC passage was machined terribly and the thing wouldn’t idle worth a crap…idle was everywhere very inconsistent. I changed everything twice. I had the customer purchase a Nick Williams TB and problem was solved. He provided the Holley TB BTW…
So I had a similiar issue…albeit not as yours…with a 6 liter build and a Holley TB. The IAC passage was machined terribly and the thing wouldn’t idle worth a crap…idle was everywhere very inconsistent. I changed everything twice. I had the customer purchase a Nick Williams TB and problem was solved. He provided the Holley TB BTW…
Thread Starter
Teching In
Joined: Oct 2023
Posts: 11
Likes: 0
Your text was printed in gray color…I fixed it.
So I had a similiar issue…albeit not as yours…with a 6 liter build and a Holley TB. The IAC passage was machined terribly and the thing wouldn’t idle worth a crap…idle was everywhere very inconsistent. I changed everything twice. I had the customer purchase a Nick Williams TB and problem was solved. He provided the Holley TB BTW…
So I had a similiar issue…albeit not as yours…with a 6 liter build and a Holley TB. The IAC passage was machined terribly and the thing wouldn’t idle worth a crap…idle was everywhere very inconsistent. I changed everything twice. I had the customer purchase a Nick Williams TB and problem was solved. He provided the Holley TB BTW…
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im going to replace my intake gaskets and retry since I can make it happen every time by just stalling the car.
if it doesn’t work still I’m going to purchase that 92mm Williams TB you said is nice.
my tuner has also reached out and said it’s mechanical and nothing to do with the tune
if it doesn’t work still I’m going to purchase that 92mm Williams TB you said is nice.
my tuner has also reached out and said it’s mechanical and nothing to do with the tune
TECH Fanatic
Joined: May 2016
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From: St. Louis
im going to replace my intake gaskets and retry since I can make it happen every time by just stalling the car.
if it doesn’t work still I’m going to purchase that 92mm Williams TB you said is nice.
my tuner has also reached out and said it’s mechanical and nothing to do with the tune
if it doesn’t work still I’m going to purchase that 92mm Williams TB you said is nice.
my tuner has also reached out and said it’s mechanical and nothing to do with the tune
Spoiler!
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The tuner has had it 3 separate times every time after a throttle body swap. He’s tuned all my friends cars with close to the same builds and cams. Same intakes and TB setups so that’s why I’m so confused. He has been doing this for a very reputable company and he’s a known good tuner.
it just doesn’t make sense if it holds a good idle then upon stalling and I start the car back up it shoots to 1500 again only if I stall
it just doesn’t make sense if it holds a good idle then upon stalling and I start the car back up it shoots to 1500 again only if I stall
TECH Fanatic
Joined: May 2016
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From: St. Louis
Why is it stalling? You mean like you were stalling it when you're trying to take off? There's a maximum idle speed value in the PCM tables separate from the regular idle tables for startup and such, if things aren't close enough it's going to have the highest idle every time it starts and then it's trying to figure itself out well enough and get down to the Targeted idle speed
It should have a strong idle, it shouldn't stall easily unless carefully modulated, that's tuning. I have a big cam and I can still start from a stop and drive the car around a parking lot with only the clutch pedal not touching the throttle. A good tune maintain the idle strongly as you load it with the clutch when it's sitting at a stop just like stock does
It should have a strong idle, it shouldn't stall easily unless carefully modulated, that's tuning. I have a big cam and I can still start from a stop and drive the car around a parking lot with only the clutch pedal not touching the throttle. A good tune maintain the idle strongly as you load it with the clutch when it's sitting at a stop just like stock does
Thread Starter
Teching In
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Why is it stalling? You mean like you were stalling it when you're trying to take off? There's a maximum idle speed value in the PCM tables separate from the regular idle tables for startup and such, if things aren't close enough it's going to have the highest idle every time it starts and then it's trying to figure itself out well enough and get down to the Targeted idle speed
It should have a strong idle, it shouldn't stall easily unless carefully modulated, that's tuning. I have a big cam and I can still start from a stop and drive the car around a parking lot with only the clutch pedal not touching the throttle. A good tune maintain the idle strongly as you load it with the clutch when it's sitting at a stop just like stock does
It should have a strong idle, it shouldn't stall easily unless carefully modulated, that's tuning. I have a big cam and I can still start from a stop and drive the car around a parking lot with only the clutch pedal not touching the throttle. A good tune maintain the idle strongly as you load it with the clutch when it's sitting at a stop just like stock does
I mean stalling like the clutch is hard to drive and I let it out and stall it atleast once per drive.
the car doesn’t stall by itself it runs great and idles good but if I stall the car by sucking at driving it
upon restart it idles at 1500 that’s the problem I’m having until I due the reset procedure it’s stay like that.
but if I don’t stall it will idle correctly
TECH Fanatic
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From: St. Louis
I mean stalling like the clutch is hard to drive and I let it out and stall it atleast once per drive.
the car doesn’t stall by itself it runs great and idles good but if I stall the car by sucking at driving it
upon restart it idles at 1500 that’s the problem I’m having until I due the reset procedure it’s stay like that.
but if I don’t stall it will idle correctly
the car doesn’t stall by itself it runs great and idles good but if I stall the car by sucking at driving it
upon restart it idles at 1500 that’s the problem I’m having until I due the reset procedure it’s stay like that.
but if I don’t stall it will idle correctly
What size engine compression and camshaft again?
How is your voltage when it stalls? My dad disconnects the battery on his '02 silverado because of a parasitic drain if it sits for too long. If he reconnects the battery and immediately tries to crank it, the idle is randomly all over the place. If he keys the ignition on once without cranking, then keys back off, then cranks it, the idle is normal. It drove me nuts trying to tune the idle on it until I realized what was happening. As long as the battery is never disconnected, or if he keys the ignition on once first, there is no problem.
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From: Bossier City, Louisiana
If I disconnect the battery, my P01 PCM's lose their memory for learned parameters and are initially tough to start and make idle correctly. But these problems resolve within one or two engine warm up cycles.
Rick
Rick
Joined: Nov 2003
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From: Wichita KS / Rancho San Diego
The car is protesting because it doesn't like being stalled. Learn to drive it and it will settle down and behave properly. 
But you say it idles at 650 or 900 when it hasn't been stalled and is behaving "normally." Well, it's not normal to have that much variation in idle speed. It should be one or the other depending on your tune. Most automatics idle at 550-650 and manuals at around 800-900.
Over the years I've had a couple of episodes of crazy idle behavior. I've posted up threads about them. In the most recent case, replacing the IAC and TPS, cleaning the MAF, throttle body, and intake had no immediate impact. But over time, the problem gradually rectified itself so that it idles normally now 95% of the time. And when it was misbehaving, when I shut it off and restarted it, like in your case, it would revert to normal (for a while).
Are you running a MAF? I've concluded that's where my problem lies although it hasn't thrown any codes.
But you say it idles at 650 or 900 when it hasn't been stalled and is behaving "normally." Well, it's not normal to have that much variation in idle speed. It should be one or the other depending on your tune. Most automatics idle at 550-650 and manuals at around 800-900.
Over the years I've had a couple of episodes of crazy idle behavior. I've posted up threads about them. In the most recent case, replacing the IAC and TPS, cleaning the MAF, throttle body, and intake had no immediate impact. But over time, the problem gradually rectified itself so that it idles normally now 95% of the time. And when it was misbehaving, when I shut it off and restarted it, like in your case, it would revert to normal (for a while).
Are you running a MAF? I've concluded that's where my problem lies although it hasn't thrown any codes.