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As carbon builds up in the throttle body of a high mileage vehicle, the ECM/PCM learns to compensate by increasing the throttle plate angle.
If enough carbon builds up, an idle surge, deceleration surge, tip-in hesitation, reduced engine power mode, and/or DTCs P0068, P0121, P1516, P2101, P2119, and/or P2176 may be experienced on high mileage vehicles.
If the throttle body is cleaned without performing an "idle learn reset/reset idle learn" with the Tech 2, the ECM/PCM may continue to compensate for previous carbon build up, causing it to return with a similar concern as well as DTCs P0121, P0506, and/or P0507.
In a similar fashion, if the ECM/PCM of a high mileage vehicle is replaced and/or reprogrammed without performing the Throttle/Idle Learn outlined in SI, the ECM/PCM may no longer compensate for existing carbon build up in the throttle body, causing it to return with a similar concern as well as DTCs P0121, P0506, and/or P0507.
Recommendation/Instructions:
If SI diagnosis does not isolate the cause of this concern, inspect the throttle body bore and plate for obvious carbon build up.
If carbon is present, follow the Throttle Body Cleaning Procedure in SI to clean the throttle body.
After ensuring that the throttle body bore and plate are clean, perform an "idle learn reset/reset idle learn" with the Tech 2 and re-evaluate the concern. This was from a Chevy TSB
 

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67 Nova, Nothin Special
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So I had a similar issue (can’t remember the exact code) on my LS3 crate motor while on Power Tour back in 2019. So the rubber line that went from my PCV catch can to the passenger side of the throttle body had swelled up and was really loose. You couldn’t tell by looking at it but it would slide right off with no resistance. I put a zip tie around it and it’s still there to this day and never had any issues or codes since. Might give that a look…
 

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Can't find any vacuum leaks and cleaned the throttle body, no linkage it is drive by wire and induction is stock
If vacuum leaks were present you would most likely also have a P0171 indicating a lean condition the ecm was trying to correct, I would try the re-learn first because I have seen that correct some really oddball issues over the years.
 

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buy a smoke machine for checking for vacuum leaks
first place to start with LS engines

I got one when having issues with my 2010 2500 6L silverado
 
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