(cold) Start up RPM

[Lviv777]

I've noticed that on normal start up rpms jump to about 1200 or so before coming down to idle. Usually same at cold start but they stay there for a few seconds. However at other times i noticed that on normal start ups the rpms jump to around 1700-1800 rpm. Any one know why? (n55 2011).

[Nkponder]

This is normal operating procedure for these vehicles. I believe it's to warm up the catalytic converter to make it work better/quicker.

If you don't like it, try MHD tune or something similar and you can delete the cold start idle.

[yco]

its normal of course..

when you try to start the car, modern cars check the air temp and many other parameters as well.. starter only cranks the engine up to 100-150rpm.. from that point ECU sends signal to have rich air fuel ratio to pick up the rev and keeping it away from stalling again.. rich air fuel mixture is safer for gasoline engines especially in first moments to heat up the engine in a linear way for not damaging the engine itself.. higher idle allows the engine to run without knocking with rich AFR when timing of ignition is being set differently in warm up phase.. things get more spicy in colder temps cause petrol gets thickened and to vaporizing it duration changes.. when combustion chamber is already in optimal temp this problem no longer exists.. in California those extreme conditions dont exist but in Lviv it does as you know..

for catalytic converters parts.. there is an emission test called cold start test.. i dont remember the exact timing of how long engine should be turned off prior to the test but its a different story.. especially in VW group engines have this.. lets say warm start, mid cold start and cold start.. when you crank to engine like in summer time after car sleeps over night, for heating up the cats fast to its optimal level of 400-500c, if engine has force induction, it even pushes some boost into idle for faster warming with rich AFR again.. thus helps to achieve less emissions stats..

[Lviv777]

Thank you guys for the explanations! Heres another question. Lets say I step out of car for 10 minutes to eat. I come back and start it up, its still warm and all, and when I start it up the RPM to go about 1800. Why is that?

[yco]

Originally Posted by Lviv777

Thank you guys for the explanations! Heres another question. Lets say I step out of car for 10 minutes to eat. I come back and start it up, its still warm and all, and when I start it up the RPM to go about 1800. Why is that?

goes up to 1800rpm for a second and goes back to normal.. you mean that?

[Lviv777]

Originally Posted by yco

goes up to 1800rpm for a second and goes back to normal.. you mean that?

Pretty much, the rpms go up way more than usual. Usually if the car is warm it usually doesn't go up above 1k but sometimes it goes to 1800.

[yco]

Originally Posted by Lviv777

Pretty much, the rpms go up way more than usual. Usually if the car is warm it usually doesn't go up above 1k but sometimes it goes to 1800.

again ECU dumps fuel into chambers more than idle requires at start up for not stalling after the start.. and actually it gives time to adjust the timing when rev is going down to idle as well.. this is more optimal if you start the car after few minutes when chamber is in optimal temp.. that usual part you re telling may include this part.. or if you inspect closer, i know California is pretty flat but even start up duration and initial revs can change on descents since gravity comes into play on fuel lines etc depends on how long car sits before the start..

after 2nd gen start-stop systems, ECU notes each pistons position for faster start and to avoid this over dumped fuel.. as you know when releasing the brakes engines comes back to life pretty fast just on the idle rev required for faster response.. cause start-stop sequence is pretty different than cold starts or mid cold starts..

[Lviv777]

Originally Posted by yco

again ECU dumps fuel into chambers more than idle requires at start up for not stalling after the start.. and actually it gives time to adjust the timing when rev is going down to idle as well.. this is more optimal if you start the car after few minutes when chamber is in optimal temp.. that usual part you re telling may include this part.. or if you inspect closer, i know California is pretty flat but even start up duration and initial revs can change on descents since gravity comes into play on fuel lines etc depends on how long car sits before the start..

after 2nd gen start-stop systems, ECU notes each pistons position for faster start and to avoid this over dumped fuel.. as you know when releasing the brakes engines comes back to life pretty fast just on the idle rev required for faster response.. cause start-stop sequence is pretty different than cold starts or mid cold starts..

Seems like that answers it! Thanks!