ive just rebuilt my head on my 1992 escort cosworth, new valves ect.. put it back together 2 days ago when it started from cold it runs perfect and drives fine but as soon as it warms up slightly idle goes up and down and its hard to drive it holds back when accelerating and slightly misses lack of power!!! its running stage 3 by the way!!! from stone cold its mint but after 5 to 10 mins it does this any one help please?? all sensors are new and timming is spot on the fault is obviousely temp related????