# Stumble in RPMs at startup



## kroelofs (Apr 7, 2020)

Looking for some help with my 2017 Cruze td. During the first start of the day or whenever it’s sat for several hours, the rpms stumble 1-3 times for a couple seconds and then catches itself. It’s done it since I got it with 40’000kms. The problem goes away and it runs perfectly after that. Outdoor temp doesn’t seem to have an effect. Looking for opinions on if this is normal or something I should be worried about. I will post a video later if needed. I apologize if I did this wrong as it’s my first post. Thanks a lot!


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## oregon_rider (Jul 21, 2017)

How many miles/km does the car have on it now?

What service has been done to the vehicle? Fuel filter? Air filter?

Have you used a good fuel additive/cleaner? It could be a sticky fuel pressure relief valve or a dirty injector.

Jeff


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## kroelofs (Apr 7, 2020)

It has 47’000kms now. Just changed the fuel filter last night. I haven’t checked the air filter but other than that it’s all up to date. I use Lucas upper cylinder lubricant every now and then but it doesn’t make a difference in the startup.


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## kroelofs (Apr 7, 2020)

oregon_rider said:


> How many miles/km does the car have on it now?
> 
> What service has been done to the vehicle? Fuel filter? Air filter?
> 
> ...


I’m also still getting good fuel mileage (52+mpg) at highway speeds if that helps narrow it down.


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## 406 (Apr 5, 2019)

Mine does it too. Has since I bought it new. 2-4 kind of lugs when it is first started. Since these puppies are electronic in terms of fuel/air control, I would think it is just a transient period while the ECM finds the correct parameters to dampen the engine to a smooth idle. Upon startup, the engine has to go from 0 rpm to some idle rpm (not 0). Ideally, this process would be critically damped, meaning the rpms don't overshoot and close in to the desired rpm (set point) as quickly as possible. Due to starting conditions usually never being the same (ambient temp, time since last shutdown, so on), the engine instead has a under-damped response where the rpms over shoot the set point, oscillate around the set point while being dampened to the set point.

Control systems.

Short answer, you're good my dude.


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## kroelofs (Apr 7, 2020)

406 said:


> Mine does it too. Has since I bought it new. 2-4 kind of lugs when it is first started. Since these puppies are electronic in terms of fuel/air control, I would think it is just a transient period while the ECM finds the correct parameters to dampen the engine to a smooth idle. Upon startup, the engine has to go from 0 rpm to some idle rpm (not 0). Ideally, this process would be critically damped, meaning the rpms don't overshoot and close in to the desired rpm (set point) as quickly as possible. Due to starting conditions usually never being the same (ambient temp, time since last shutdown, so on), the engine instead has a under-damped response where the rpms over shoot the set point, oscillate around the set point while being dampened to the set point.
> 
> Control systems.
> 
> Short answer, you're good my dude.


I was leaning towards it just being the electronics figuring everything out, but thought I’d check with other owners. Thanks for the help.


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