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I thought I had this issue resolved a few months ago, but I find it still happening periodically. I will be making an appointment to have it checked out soon but wondering if anyone else has experienced this. Vehicle leaps forward (or reverse), on start-up when I put it in gear and remove my foot from the brake, as if it was revving too high, but I’ve seen it happen at 1 grand which I believe to be a normal idol. I have also noticed that at times after it’s been through its warm-up ritual the tach will still sit slightly over 1 grand and at times it will have no affect and others it will. If I am in a tight parking spot this “leap” could cause me to hit a car in front of me, or worse a pedestrian. At first I thought it was because I was putting it into gear while it was still going through its start-up ritual. Turns out that is not the case, I have intentional put it into gear while it was in this phase and the vehicle went into gear normally, I’ve been monitoring this very closely the last couple of months and cannot determine a pattern, it seems to happen randomly. It will happen even after a minute or two warm up. It happens very infrequently, maybe 1 in 40 or so starts. The leap is not very aggressive, but enough to get your attention. I have a feeling this will be one of those cases where the dealer cannot duplicate the issue and tells me that everything seems to be working fine.
Mine did it today.The idle was around 1.5 that is on the high end for idleing
 

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2021 Trailblazer RS
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Nice to know this issue isn't isolated to my vehicle, curious to find out if anyone else here has experienced it. I'm hoping the dealer may have seen others come in for this problem and determined a fix, I know I'm being overly optimistic. Maybe as more of these SUV's get out into circulation someone will figure it out. I guess these are the bugs that come along when purchasing a vehicle fist year out.
I’ve been noticing this in mine and I’ve had it since July. Doesn’t happen all the time, just sometimes.
 

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I’ve been noticing this in mine and I’ve had it since July. Doesn’t happen all the time, just sometimes.
After reading your post I paid more attention to my "start up". My tach also will sit sometimes at 1.5, close to 2, but other starts just idles at 1. I have been wondering if the "leap" is more associated to how we turn off the vehicle and how it affects the next start up. I generally leave the "auto stop" feature on. So when I park in my garage for example, I pull in, stop, and the vehicle goes into auto stop before I put it into park and then take foot from brake. So maybe the next time I start it, the start up is somehow affected by fuel in the fuel line or engine that was there when it went into auto stop and it also gets a boost of fuel from normal startup. Another theory I wonder about is this. My trailblazer, and others have reported the same, when you open any passenger door, or even the tailgate, after the vehicle has been sitting for a while, will make a "motor" noise (almost a whining sound) for 3 or so seconds, coming from the rear. It doesn't happen if the vehicle has sat for a shorter time. Someone wrote in this forum that the noise is the fuel pump in the rear, sending fuel to the engine for starting. That GM calculated if you are opening a door you are likely to be starting the vehicle. So maybe it is this fuel boost that is causing the "leaping" and higher temporary rev of engine. And this is when we get the leap. I find the noise aggravating. 2022, and they design a car that makes this noise when you open a door but only after sitting a while. They couldn't find/make a fuel pump that was more silent and not sound like something that bought at a flea market?
 

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The "leap" does seem to be associated with where the rpm's are at. on a cold start mine will start around 1.5 and if shift immediately (which is extremely rare for me) then there will be a leap. but if i allow the tach to settle down below 1 then its fine. It only takes about 30-45 seconds for the tach to settle down after a start. So i would really just pay attention to the tach before shifting.
 

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The "leap" does seem to be associated with where the rpm's are at. on a cold start mine will start around 1.5 and if shift immediately (which is extremely rare for me) then there will be a leap. but if i allow the tach to settle down below 1 then its fine. It only takes about 30-45 seconds for the tach to settle down after a start. So i would really just pay attention to the tach before shifting.
I have started to do similar. The moment I get in car I start it. Then I put on the seat belt, adjust radio, that type of thing. By that time, when I'm ready to put it into gear, the tach has settled to around 1.
 

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GM needs to do a software update to fix this. It's as simple as when it sees the brake signal lower RPM. As soon as I can get into the ECM I may adjust it.
 

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GM needs to do a software update to fix this. It's as simple as when it sees the brake signal lower RPM. As soon as I can get into the ECM I may adjust it.
Agreed they really need to resolve this. Would solve my biggest gripe with the vehicle, is somewhat embarrassing if you do it with a passenger... suddenly you're jerking back and forth like you're hamming on the brakes and don't know how to drive... lol

It doesn't occur when shifting directly into reverse while the tach is doing it's diagnostic.
 
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