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