TPS, Alternator, Trans, or Other

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Prometheus_Lens

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Aloha to all. I apologize up front if a topic like this exists on the threads and I missed it. I might have overlooked a possible answer while searching the forums, but I have to ask it. I own a 2011 Tahoe LT, 5.3L, with 132,000 +/- a few miles. While I am in Park, the idle is at 600 rpms. However, while in gear, I am at 500 rpms while sitting at a complete stop. However, my Tahoe likes to dip a little under 500 rpms while decelerating (around 480 or so). Also, the transmission gets an unusual bump in rpm speed while I am slowing down to a stop as it goes from gear to gear.

What I have considered is this... 1) Is it the TPS that is going out and causing a bad output signal to the ECU; further causing a miss read in the transmission solenoid... 2) Is the alternator the issue because it is showing symptoms of not holding a charge on deceleration... 3) It is the transmission solenoids showing signs of down-shifting malfunction???

Again, I have already removed the Throttle Body and cleaned the crap out of that and the intake plenum. In the end, what I am trying to correct is low rpms while in gear, and low rpms while downshifting to a complete stop.

Thank you and standing by...
 

Brandon2489

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From my experience this is all normal behavior with the idle speed and clunky trans while decelerating and coming to a stop. There may be an issue with your motor mounts or front differential mounts causing the clunks but in my case the clunks are part of the TCM learning your driving habits. I ended up getting a tune on my Tahoe and I have the idle speed while in drive but stopped at a light set to 600-625. The idle speed is set the same for idle while in park. These engines just don't like the low idle speed set from the factory in my experience. Also after the tune the clunks disappeared due to TCM being tuned also but keep in mind you can not turn anything off in the TCM to not learn your driving habits. It will relearn haha. When I start to notice clunks after awhile I usually just drive the tahoe a little harder (more gas pedal) for about 2 days. It will learn a new driving pattern and be fine for months. Some people don't have an issue but from my experience the people that tend to drive in lots of neighborhoods and need to go slow tend to have the clunking issue more so than people that drive aggressively most of the time just due to the TCM learning habits. By all means though make sure you don't have any parts failing first. It's not out of the ordinary for them to fail. Just want to make sure I'm clear in that a tune is not a fix all for clunks.
 

Brandon2489

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Also do you have a check engine light or any other lights alerting you to a problem?
 

Doubeleive

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if it is something it has started doing and has not been doing it in the past then maybe the MAF (mass airflow sensor) is getting goofy, it controls the shifting based on airflow, it could also be the transmission or even possibly something else. I hate to tell people to just throw money at there vehicles but unless you have a scanner that can read live data then it's a gamble of possible bad parts -vs- cost of a diagnostic to confirm. funky idle could be because of the MAF as well or it could be low fuel pressure or dirty injectors or a combination of all, hell it could even be a bad ground or wire harness.
 
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Prometheus_Lens

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if it is something it has started doing and has not been doing it in the past then maybe the MAF (mass airflow sensor) is getting goofy, it controls the shifting based on airflow, it could also be the transmission or even possibly something else. I hate to tell people to just throw money at there vehicles but unless you have a scanner that can read live data then it's a gamble of possible bad parts -vs- cost of a diagnostic to confirm. funky idle could be because of the MAF as well or it could be low fuel pressure or dirty injectors or a combination of all, hell it could even be a bad ground or wire harness.
Truth be told, I just recently purchased my Tahoe about a month ago. I didn't consider the MAF yet. I also did a sea foam cleanse on my fuel system already.
 

Fless

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In addition to the previous suggestions, especially @Doubeleive's MAF comment, has the IAC been tested and is working correctly?
 
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Prometheus_Lens

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In addition to the previous suggestions, especially @Doubeleive's MAF comment, has the IAC been tested and is working correctly?
I did consider that first. On an earlier Tahoe maybe. But there are a few sensors tied in to the TPS. I am considering replacing it like I mentioned, but want to reach out to the forum world first before making any unnecessary purchases.
 

Foggy

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TPS is integrated into the throttle body
You want to use a scan tool of some sort to look at your TPS vs Throttle vs Commanded
values, IF you think that's an issue.

You may really just need some good old fashioned TLC
Spark plugs, plug wire, air filter, belts, trans filter/fluid, differential fluids.
If this is a new to you truck, then get all the maint done before you start
chasing ghosts and looking for problems
 
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