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Cold Start Problem - Lost 1 - 1.5 MPGS

Hi, I posted this a while back but came upon a new discovery. I had posted earlier that my truck seems to run rough when I start it in the mornings. Its a 2002 Chevy Z71. 327 Engine. 60K miles. It didn't start doing this until it got cold out side. When I start it, it idles up and then when it idles back down it sputters. It doesn't quit. It threw an error code and I had it checked and it just said "Random Misfire" Once it warms up a bit it stops doing this. Also if I let it sit for a few hours and cool back off it doesn't do it. It only seems to do this when I let it sit overnight. I tried replacing the fuel filter, put gas treatment in it and replace a sensor on the side of the block. I can't remember the name of the senor but I believe it was IAC or something like that. I know it checks the temp of the block. The new discovery I made the other day was that it has lost mpg. I used to get around 15 during my usual driving. Now it get a little over 13.5. Any ideas would be greatly appreciated. Thanks Josh

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Jre1229
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Yeah gasoline you buy at the pump when its 80 degrees outside, is not the same gasoline you buy when its 32 degrees every where in the country. And the winter grade delivers less mileage. Your drop is about in line with what others have reported. IAC is Idle Air Control Valve and its located on the throttle assembly if you vehicle has one. Temperature sensor measures block temperature, located in intake manifold. Only sensors I know on the side of an engine, knock sensors, and some vehicles have a crank sensor. For the sputter/miss I would be looking at plug wires and or plugs Whitelightning

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Whitelightning

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Jre1229

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ShoeSaleman

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