Sometimes the idle control valves freaks-out at idle and create situations as you have described. Especially if a cam has been fiited. You could try disconnecting the idle control valve to see if the condition continues. If not, its related to the ICV. Sometimes they can be oversensitive and cause the revs to stay up after you use the throttle, usually at about 1300rpm for a few secs. You can stop this by making a plate from some thin aluminium that fits under the ICV and has holes only a few mm in dia where the big ones are.
i would check KIWI3D's suggestion...a common fault, often demostrates itself as hard to stop when going slow (like pulling up to the lights) and gives the feeling that the car is trying to outdrive the brakes.
Another common item is the throttle cable. Where it passes over the rocker cover it clips on. It is common to break there and prevent the accelerator from being fully released.