My father has a 1994 GMC Jimmy with a 4.3 vortec. The problm is that when its cold it idles very poorly. It seems to be a consistent misfire in my opinion. When gas is given it runs fine but when gas is let off it will do it again. THere is also some unburnt fuel that is getting pumep out. He has has everything on it changed electronic contorl wise and I dont want him spending more money. I hope you can help.