My buddie has a 97'ish s10 blazer 4x4 with a vortec 4.3L. when he starts it, it runs spurattic. The idle jumps around a bit. Also, it is puffing blueish smoke. I know that its not burning all the fuel, but not sure why. When it gets warm, it goes away. It failed smog by what he called "bad low idle emmissions". My guess is a bad cold start valve, but I don't know if those trucks even have that. Any Ideas??? Any ideas are greatly appreciated.