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      04-07-2011, 09:18 AM   #1
poiney
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Question 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, 10:08 AM   #2
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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.
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      04-07-2011, 10:16 AM   #3
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Quote:
Originally Posted by roundel335 View Post
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.
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      04-07-2011, 10:21 AM   #4
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Quote:
Originally Posted by poiney View Post
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.
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      04-07-2011, 11:29 AM   #5
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Like other have already explained...
But I'm curious what was your previous car??
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