1994 Ford GT Mustang Cold mornings engine idle problems

On cold mornings after starting the car, the 302 engine runs smooth for about 30 seconds and then it starts surging up to about 2000 rpms and drops to 500 rpms. This goes on until the engine stops running. Some cold mornings the engine will run fine for 30 seconds or so then just stop like someone cut the ignition off. On the 2 situations it this does not occur everytime. During these occurances, if I start the engine and stay with the car keeping the rpms about 2000 for 30 seconds or so, engines runs fine. This only happens when engine is cold. The idle sensor and throttle position sensor has already been replaced and did not solve the problem. Also another problem has started occurring. Now when it is warm and changing gears, the engine will idle up and sitting at intersections the engine cuts off unless you keep the rpms up.