sounds like its your ebpv closing for faster warm ups. once the truck it up to temp does it still do it?Need some help! My 97 will start in cold weather, but when I start to drive its seems as if it is struggling for air and produces a much louder sound under the hood. I have checked connections both air and electrical and could not locate any obvious issues under the hood. Air filter is new and I recently had the glow plugs replaced and pcm replaced. I only encounter this problem in cold temperatures 45 and below and while driving. The sound and rough running will decrease if I increase my speed, but it will return as the speed is reduced. When in park or stopped I don't encounter the problem.