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My car used to at first crank in the morning go to a high rpm for a few moments that sounds like a jet engine. Then it would drop back down to normal rpm and that was when I would put in gear and drive off. Everything good. Now the weather is in the 30's-40's and I crank and it never goes into jet engine sound mode. Is that normall? Only had the car a year and have never noticed this before. I don't want to damage the transmission by taking off too early. I read the owners manual and found nothing on this. Any advise what to do? How long should I let it run on cold mornings? Thanks
 

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That 'jet engine sound' was likely not your engine but the secondary air injection pump. It turns on and runs for roughly 30s to warm up the cat and sounds like a mean Hoover. It doesn't turn on in wintry temperatures. So unless your tach used to shoot up high (provided you have one), this is normal. :)
 
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And there would be no harm to the transmission by pulling away right after startup. For years it has been recommended not to allow an engine to “warm up” before pulling off as this increases pollution. It is ok to allow the engine to run for several seconds on cold starts before taking off though.
 
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