Thanks for the repost scdriver. I was bragging how good my car was running now after a couple of days of the new CTS, but this morning I get in to drive to work, go about 1/4 mile out of the subdivision up to the stop sign and wait to pull out. When I do I get a big double hesitation and then it goes on and runs perf. On the way back home I stopped 2 blocks from work and take off with the AC on and its fine. This morning I had the AC off. It seems like if I set and idle to long is usually when I get the hesitation from stop.
I swapped out the coolant sensor today, pretty easy job, just have to get the coil pack and spark plug wires out of the way. Original sensor had 194k miles and was clean, no corrosion at all, thanks to Dex-Cool (I know, a lot of complaints of this coolant, but working for me).
I did measure the resistance of the old and new sensor using a Fluke multimeter at 80F:
Old = 2050 ohms
New = 1650 ohms
Now that's quite a bit of difference. According to the services manual, the resistance of the sensor goes down as temperature goes up. So my old sensor was telling the ECU the coolant was cooler than it actually is causing the ECU to richen the mixture? That's the theory anyway. The chart in the service manual is not exact, has a wide zone of acceptable resistance range at a given temperature, and not the easiest to read the acceptable limits.
I'll report back after a couple of tank fulls, see if MPG goes up.