I have a 2004 Chevy Duramax 6.6 that has developed at surge at idle. started very light but I currently get a constant surge of approx. 200 rpms about every 3 to 4 seconds. No surge on cold start, but once it warms to operating temp. the surge begins. Can be felt slightly while driving. Just replaced the fuel pressure sensor on fuel rail and same thing. I could monitor FP on my snapon modis and can see fuel pressure increase at the same time it surges. Any Ideas anyone.