I have a 190e 2.6 with a 5 speed I bought in April and I've noticed there is a slight throttle lag that makes smooth shifting a little difficult. I’ve also noticed when I close the throttle the engine doesn’t slow down right away. Is this a characteristic of this fuel system or is it an indication that something is wrong and hopefully can be fixed or adjusted.

If the idle doesn't settle down quickly, you do have a problem in the idle control system. I would have it checked out.