My 03 Envoy 4.2L I6 has 130k miles on it. I had the dealer do the plugs and tune up at 110k. For a while now every 2 out of 3 times I stop to get gas I get a high idle 900 ish RPMs. I never get the CEL on the dash. I have a cheap code scanner and it shows p0172(bank 1 running rich). I clear the code and drive fine with normal idle till i need to stop for gas again. I went to the dealer and got a new gas cap (original GM part). This seemed to help for about a month but back to the same issues. Its odd that I can drive 200 to 300 miles and not have any issues but when I stop for gas things get weird. Also i find it odd the CEL light never lights. I know it works because I had the thermostat go bad and it lit for that. Any thoughts on it? This Envoy is in outstanding shape other than this code and its starting to annoy me to the point of taking it to a mechanic to get fixed but I thought I would see what advice you guys can give me before I do that. Thanks again for any help!