So I bought this Mazda protégé5 needed a head gasket.put a new head gasket on brought it to an engine shop who then did a valve job and Plained the head .I also put a new timing belt on and did everything correctly when installing .so here's the problem, I just put every thing back together and started it up and it started and ran like new!a lot better than when I bought it. So I let it run for about 5 minutes after the first start a haze of smoke started to apear near the valve cover and I could hear something when I put my ear next to it that didn't sound right almost like a rubbing sound?now everytime i start it ,it won't stay running without holding the gas peddle down and when you take your foot off it quits. .. any idea what might cause this?