The choke is controled by the computer system on board. It is refered to as tickover. That is where the idle drops to its normal 750-500 rpms.
Yes oil weight does help in cold starts. The problem is with a warm up at idle the oil presure stays low. The presure must build up to insure proper flow. If the oil does not flow well it will stay cold and thick. Remember circulation is key in keeping the oil at the right tempeture. If it does not than you will have cold oil setting in your oil pan.