High idle and engine does not decelerate

Good morning,

Did you change the throttle body?

https://www.2carpros.com/articles/engine-idles-too-high

https://www.2carpros.com/articles/throttle-actuator-service

Can I have the code that was set?

https://www.2carpros.com/articles/reduced-power-limp-mode

I would start by doing a relearn for the idle.

Roy

#PIP4578B: SES Light Idle Surge And/Or Reduced Engine Power Mode With DTCs P0068 P0121 P0506 P0507 P1516 P2101 P2119 And/Or P2176 - Clean Throttle Body And Perform Idle Learn Reset - (Dec 18, 2017)
Subject: SES Light, Idle Surge, and/or Reduced Engine Power Mode with DTCs P0068, P0121, P0506, P0507, P1516, P2101, P2119, and/or P2176 - Clean Throttle Body and Perform Idle Learn Reset image
Models: 2007 Buick Rainier
2007†2018 Cadillac CTS-V,
2007†2018 Cadillac Escalade
2006†2014 Chevrolet Avalanche
2010†2018 Chevrolet Camaro
2006†2018 Chevrolet Corvette
2008†2009 Chevrolet Colorado
2006†2017 Chevrolet Express
2006†2009 Chevrolet Impala
2006†2009 Chevrolet Monte Carlo
2006†2018 Chevrolet Silverado
2006†2018 Chevrolet Suburban
2006†2018 Chevrolet Tahoe
2006†2009 Chevrolet Trail Blazer
2008†2009 GMC Canyon
2006†2009 GMC Envoy
2006†2017 GMC Savana
2006†2018 GMC Sierra
2006†2018 GMC Yukon
2007†2008 Hummer H2
2008†2009 Hummer H3
2007†2008 Pontiac Grand Prix
2008†2009 Pontiac G8
2006†2009 Saab 97x
With a V8 Engine
This PI was superseded to update model years. Please discard PIP4578A.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
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.

Notice: Depending on the vehicle you are working on, the "idle learn reset/reset idle learn" is normally found on the Tech 2 ECM menu for Module Set Up or Special Functions/TAC System.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

GM bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

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