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?

 

[BG1988]

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.

and you will be chasing a problem that doesn't exist..

it's normal, it's decel fuel cut-off (DFCO). DFCO goes away around 15-18 mph ish try power stopping at that point see if it still does it..

the issue is the person behind the wheel, Increase following distance while driving should correct the problem ...

Mine started doing this when the hybrid battery went.. i know you don't got one i figured out it was the DFCO causing it.... as normally it would regenerate and/or drop to 1,000rpm EVT gear on regen instead of needing the ICE, power to stop...


I tested it in neutral gear which such (DFCO) doesn't occur (note i got a AUX pump don't attempt this on your vehicle as it may damage the transmission... )..

if anything the fuel injectors are slow/lazy , which might cause the engine to slow too much i.e dropping to 700rpm while stopping..

 

[Hodgeee]

 

[Hodgeee]

I will try the braking procedure and let you know. Its not a big problem, just annoying, and only happens when i have to break quickly for some reason. It did it before the new fuel injectors, I forgot to list that, but I put new AcDelco Pro injectors in also, same affect. If this is normal, than I will let it go, or research into DFCO turn off maybe.
Since renewing all the parts, it still drops rpms, but it has never acted like it was going to stall, or even shakes that much when it does drop rpms. Under normal breaking, your right, it acts totally fine. Thanks for letting me know about DFCO, was unaware that the vehicle even had that. Plus the dealership didnt give a reason, they just stated its normal. Since I bought this with almost 150,000 miles, thats why I replaced all the parts I did, something I always do with vehicles when they hit this mileage, except for my Toyotas. Out of 30 vehicles ive owned, never been stranded(keeping my fingers crossed)!

 

[BG1988]

Did you do the rear diff and transfer case fluids?

i have to do mine (rear diff)

my dads Chevy sonic does this bump as well while stopping the corolla does it as well mildly though..

 

[Doubeleive]

ya, I would maybe consider replacing the throttle body at this point, I drive mine like a race car and it doesn't do this.
OR try and drive record the live data from the throttle body, it could be in spec "electrically" but maybe not mechanically
I don't know if something like that would show up in live data or not.
could still be something else entirely though but that's what I would do next.
if this DFCO has kicked in on me before it would be extremely rare, I suppose it perhaps has dipped to low idle once or twice in the last 5 years but that would have been me causing it by doing some aggressive combo of gas/brake/dip or something extreme.

 

[Hodgeee]

Trying to find a cheap throttle body at the pick a parts, to test this and not spend more money if not needed. Went this morning, every time i find a chevy its stripped, tons and tons of Fords, and Dodges though. Dealership said they tested it. And yes All fluids changed the day after purchased. Since it causes no problems except annoying me, i might just leave it alone. Will report on other tests.

 

[BG1988]

ya, I would maybe consider replacing the throttle body at this point, I drive mine like a race car and it doesn't do this.
OR try and drive record the live data from the throttle body, it could be in spec "electrically" but maybe not mechanically
I don't know if something like that would show up in live data or not.
could still be something else entirely though but that's what I would do next.
if this DFCO has kicked in on me before it would be extremely rare, I suppose it perhaps has dipped to low idle once or twice in the last 5 years but that would have been me causing it by doing some aggressive combo of gas/brake/dip or something extreme.

i already tried a new throttle body on mine.. nothing changed

i suspect it could be electrical related.. i.e dirty ground wire to the injectors... but i'm circling in on something to do with the injectors you can see it has 3 ground points... 3 points of failure

 

[Doubeleive]

i already tried a new throttle body on mine.. nothing changed

you have also reported other unexplainable, questionable, bizarre things with your vehicle before,, plus it's a hybrid.

 

[BG1988]

you have also reported other unexplainable, questionable, bizarre things with your vehicle before,, plus it's a hybrid.

were talking about engine rpm dropping that would have nothing to do with the transmission. unless something is really fudged up with it..

it only specifically does it on a DCFO event and not in M4,M3,M2,M1...

that means the rpm is dropping under load...

 

[BG1988]

you have also reported other unexplainable, questionable, bizarre things with your vehicle before,, plus it's a hybrid.

i read your post here, it reminded me about some damaged engine wire harness loom (in the rear area of the engine) not wires just the plastic tubing that was brittle and breaking apart

i was able to replace some of it with genuine GM tubing

it's a good reason to suspect ground wire issues