I have a nissan serena 1.6 petrol reg 1997. When car is cold it starts fine and runs OK.when car warms up I get a hunting feeling when I change up gears.once it has been in a gear for a second or two it runs fine till neat gear change. Has anyone any ideas to what's doing this and if so how can I solve it.

You can try cleaning the throttle body with carb cleaner and also use an additive in the tank to help clean your injection system. Try those first.