My 1993 190E 2.6 does not want to shift unless it is allowed to idle about 45 secs. to one min. before moving. Without this short warm up period, it just holds 1st gear. With the short idle period, it will drive away and shift perfectly. The fluid level is full and does not appear or smell burnt. Does this sound like a trans problem or could it be a sensor or some other cause. Any theories would be appreciated. Thanks