Rpm drop when stopping.

[Hodgeee]

Ok, I know this has been discussed before, but after all my reading, I cannot find an answer to my particular problem. 2013 Tahoe Lt 5.3 flex fuel 146000miles. When about to come to complete stop, at medium to hard braking, rpms drop to 350 to 400rpms from the 550 idle. Did all the normal stuff, cleaned and tested throttle body and maf sensor. New plugs, wires, coils, fuel pump, vapor canister and pump, vapor solenoid, map sensor, O2 sensors. Tested cats, and even put truck in nuetral in case the torque lockup release was slow, still does it like day one. 4 corner complete brake install, everything good. Stealership tested the booster and said no problems, no codes, this is normal. Did all this since new to me within 5000 miles. Runs great now, picked up 3mpg, gets 13 city and 19, 20, on freeway, like new. I dont think 200rpm drop is normal though. Was thinking either computer, or crank, camshaft position sensors, but it runs so good. I use to be a mechanic 30 years ago, but no professional work since then. I am stumped, im usually the guy everyone comes to when they have problems. Anyone else have any ideas? Did I miss anything.

Lastly it did show lean both banks, no code, only when Chevy mechanic friend ran it with dealership scanner. This went away with all the work.

Any help or extra ideas appreciated.

 

[Dustin Jackson]

Help me understand the problem, the problem happens when coming to an aggressive stop and what happens is the RPMs dip down really low? Do the RPMs dip low for a moment or do they stay really low until the next time you stop?

And you attempted to brake aggressively in neutral and the same thing happened?

 

[strutaeng]

Could it be a harsh downshift? When I was riding with my former coworker on his 2017 Silverado with the 6 speed I noticed coming to a stop it shifted harsh, but I didn't say anything because I'm not really familiar with the way the 6 speeds operate. His transmission eventually failed a few months ago at 104k. It got rebuilt and he said it runs good now. I'll have to ask him about the downshifts.

My wife drives a 2020 Express Van with 6 speed and I notice the few times that I drive it it downshifts before coming to a stop. It only has 16k miles, so I'm assuming that's the way it's supposed to work.

 

[Hodgeee]

It dips down for just a moment then returns to normal idle, this only happens for a second, at that point it shakes a little, and sometimes the lights all get dim for a second also, but rarely. Only on medium to hard breaking.

Does it in nuetral also, forwards or backwards, but you really got to mash the brakes for it to react in reverse. Also when shifted into nuetral in reverse also.

 

[Hodgeee]

Forgot, all parts are AcDelco or GM original

 

[Hodgeee]

No tranny is in great shape, no hard or aggressive shifting.

 

[Dustin Jackson]

@Hodgeee Doesn't seem to be too big of a problem but annoying nonetheless. I wonder if there is an electrical problem like a cable that shifts under harsh braking.

 

[Hodgeee]

Has never caused an issue, but yes annoying. I did go over every electrical connection and bracket. Seems fine, but i wonder the same. I looked up the carfax report, and the throttle body was replaced 9000 miles ago. Checked it, aint an oem part. The GM or AcDelco have the part# stamped on the side, along with the brand name. This one has no markings. The throttle position sensor could be a little off. Ill check this also and let you guys know.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving clarifying questions from the knowledgeable folks on this Forum.

 

[mikez71]

brake booster hose maybe?