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Old 04-04-2009, 10:07 PM   #1
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Cold morning starts

Quick question, when I start my car up in the morning and drive it the first 2 minutes, as soon as I let the clutch out and go into neutral, the revs drop very slowly. This only happens the first minute or so after I start the engine in the morning though. Is this natural because of oil temps or is there something else involved?

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Old 04-05-2009, 03:04 AM   #2
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That sounds about right. The transmission oil hasn't heated up yet. How cold is it? My old Honda at 20F or below would do the same. That was only a 1.6L turning a 5 speed.
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Old 04-05-2009, 09:00 AM   #3
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That's normal behavior for just about every car on the market.

What's happening is that when you first start the car, the computer sees that the coolant temperature and the O2 sensor temperatures are low. It sets a fairly high idle speed in order to heat up the O2 sensors, and bring the coolant temperature into the normal range as quickly as it possibly can.

As the O2 sensors warm up, and start to give the computer useable data, the computer starts to lower the idle speed as it controls the mixture in a closed loop cycle. The idle speed starts to come down. But, the computer still sees that the Coolant temperature is still lower than the normal range, so it still keeps the idle speed higher than normal.

Once the coolant temperature reaches the normal range, then the computer drops the idle rpm to where it belongs.

BC.

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