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2002 GMC SIERRA STARTS GOOD THEN IDLE DROPS SO LOW THAT IT…

2002 GMC SIERRA STARTS...

2002 GMC SIERRA STARTS GOOD THEN IDLE DROPS SO LOW THAT IT USUALLY DIES; WHEN IT DOES DTAY RUNNING, AFTER 15 SECONDS OR SO IT RUNS FINE.

Mechanic's Assistant: How many miles are on the car? What size is the engine?

260,000 4.8

Mechanic's Assistant: Are you fixing your Sierra yourself? What have you tried so far?

CLEANED MAF, CHANGED AIR FILTER, CHANGED TPS

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Answered in 9 minutes by:
11/19/2017
Pete
Pete, GMC Mechanic
Category: GMC
Satisfied Customers: 32,878
Experience: GM training and dealer tech for 14+ years. Diagnostics
Verified

Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

If you didnt clean the throttle body this needs done.To do this remove the air intake tubing from it and take a rag with some carb. cleaner or brake cleaner sprayed on the rag and wipe out the throttle body bore opening the plate in the throttle body by hand wiping it clean as well.Small carbon build up in the bore and on the plate causes this issue.There is also a bulletin on this model to clean the throttle body and have the PCM ( engine and transmission computer) programming updated for this fault.The bulletin number is ***** .The programming usually has to be done by a dealer with their computer.

The other issue this engine has is the intake gaskets.They shrink and leak allowing excess air.This usually affects the most when the engine is cold then is fine when warm.GM re designed the gaskets to be replaced to resolve this fault.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service,your 5 star rating is appreciated ( should be a link to click on here or above).You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

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Customer reply replied 7 months ago
Thank you, I'll try that.

Your welcome

Let me know if you need anything else and feel free to rate my help here or above ( should be a link to click on ) as this is how I receive credit for my time,this can be done at any time and you can still come back here and reply if needed.Your 5 star rating is appreciated

Thanks Pete

Pete
Pete, GMC Mechanic
Category: GMC
Satisfied Customers: 32,878
Experience: GM training and dealer tech for 14+ years. Diagnostics
Verified
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Category: GMC
Satisfied Customers: 32,878
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