I have a 1.2cc 52 plate Ford Fiesta with a zetec engine. It starts great, first time every time, my problem starts as soon as I start to drive. As I'm driving it judders/kangaroos down the road and doesn't stop until the engine warms up which is around 15 minutes into the journey. It's allot worse when the weathers cold and really bad when it's cold and wet. The only example I can think of to describe it is if you go back 20 years and cars had manual chokes, and if you didn't get the choke pulled out the right length then the car would stutter down the road until the choke was positioned correctly. So because the symptoms are similar to a choke related issue I was wondering if there might be a problem with the automatic choke? If it is, where are they positioned? Is it a big job to fix? or is it nothing to do with the choke? Somebody mentioned a cold release valve but after I Googled "cold release valve" problems, all of the results showed the cars not starting correctly, but mine starts without any problems. So I'm stumped and any help with my problem would be really appreciated. If I missed any information out and you need any more to help solve my problem then just ask, thanks.