I just got an 05 CTS from a car lot the other day and after new plugs, maf sensor cleaner, and new oil, most of the codes have disappeared. The only one I'm concerned about now is p2008 History/Current- intake manifold runner control valve circuit/open. I drove it bout 65 miles round trip on highway to locksmith for extra keys and remote programming and at 62 to 65 mph, could not get it above 21.2 mpg. Cant find the solenoid online xcept at gm for 70$. Rock and Summit has em for 07 on, and Alldata shows what it looks like. I wonder what's up with that? I wonder, can these valves be cleaned? And do they make that much difference in mileage? I'm hoping maybe if I clean the valve or get a new one it will better my mileage? Anybody know about this stuff? Car runs absolutely great! I love it. Thanks for any replies!