why does engine rev faster for the first minute?

poiney · 04-07-2011, 08:18 AM

What is happening during this time frame that changes the idle RPM and why is it designed this way?

For example, I don't recall my previous car changing idle like this. I believe this occurs for both 328 and 335.

RoundelM3 · 04-07-2011, 09:08 AM

It's called "warmup" and the computer does it. The mixture is set richer and idle speed increased to get the oil and internal parts up to temperature quickly. Cold engines don't idle very smoothly. In the old days of carburetion, either a manual or automatic "choke" was used to do the very same thing.

poiney · 04-07-2011, 09:16 AM

Quote:

Originally Posted by roundel335

It's called "warmup" and the computer does it. The mixture is set richer and idle speed increased to get the oil and internal parts up to temperature quickly. Cold engines don't idle very smoothly. In the old days of carburetion, either a manual or automatic "choke" was used to do the very same thing.

Thanks. I thought that all cars have an automatic choke, but I didn't recall that they changed idle speed. It seems like an easy feature to incorporate if its helpful for extending engine life.

JSH3 · 04-07-2011, 09:21 AM

Quote:

Originally Posted by poiney

Thanks. I thought that all cars have an automatic choke, but I didn't recall that they changed idle speed. It seems like an easy feature to incorporate if its helpful for extending engine life.

Every car I've ever owned ran at a higher idle rpm at startup until a minute or so passed. Nothing new to me.

marv85 · 04-07-2011, 10:29 AM

Like other have already explained...
But I'm curious what was your previous car??

04-07-2011, 08:18 AM	#1
poiney Captain 36 Rep 798 Posts Drives: 328i coupe Join Date: Dec 2006 Location: SJ iTrader: (0)	why does engine rev faster for the first minute? What is happening during this time frame that changes the idle RPM and why is it designed this way? For example, I don't recall my previous car changing idle like this. I believe this occurs for both 328 and 335.
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04-07-2011, 09:08 AM	#2
RoundelM3 Major General 1837 Rep 6,990 Posts Drives: 15 F80 M3, 22 G01 X3 30i Join Date: Apr 2010 Location: Clayton, NC iTrader: (2) Garage List 2022 BMW X3 [9.83] 2015 BMW M3 [6.50]	It's called "warmup" and the computer does it. The mixture is set richer and idle speed increased to get the oil and internal parts up to temperature quickly. Cold engines don't idle very smoothly. In the old days of carburetion, either a manual or automatic "choke" was used to do the very same thing. __________________ 2015 F80 ///M3 Sedan 7DCT Tanzanite, 2022 X3 sDrive30i 8AT Brooklyn Grey
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04-07-2011, 10:29 AM	#5
marv85 Colonel 70 Rep 2,626 Posts Drives: '07 E92 335i MT Join Date: Jun 2010 Location: Bay Area iTrader: (7)	Like other have already explained... But I'm curious what was your previous car?? __________________ '07 E92 335i 6MT- HP650, inlets/outlets, ER FMIC, VRSF CP, LPFP stg2, CSF rad, 'is Aux rad, ER OC, Ohlins, M control arms, eibach front sway bar. '05 C55 AMG SOLD - '22 Tesla M3P \| '10 E92 335i M, 6MT COBB, FBO, st2 LPFP, Mfactory LSD \| '07 E90 335i, PTF COBB E50, FBO, HFS4
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