Probably not the cause... but I had very similar problems when my throttle cable was on its way out!!
high idle, bogging down/jerking once warm, revs felt really slow and it was only once the car had warmed up?!!?
After fitting a new one the car felt completely different, much more eager and all the rev/idle related problems where cured
Only £18 for a new cable, did you fit new when installing the engine?