I'm calling the dealer tomorrow to schedule an appointment, but I'd like to go in with some info first.
This is repeatable, and it's not spinning tires (had people observe it).
On a cold start , if I give it more-than average gas from a dead stop, my 06 CTS starts acting like a bucking bronco. Fast accel, no accel, fast accel, no accel. It's almost like everything cuts out or the transmission disengages. The Tach drops from around 3k to 1.5k when I "buck."
Repeatable conditions:
- Cold start (like in the morning). But idling for 5 minutes doesn't help
- From a Dead stop
- Faster-than-average acceleration (to merge onto street), but not fast enough to spin tires. Note: Had people observe on the street, no tires spinning.
- Temp/humidity can vary. Recently at 72 deg F w/ no humidity
It almost feels like it's a shifting problem, but I don't know enough to say. My dad says it might be a sensor, but newer cars are beyond his scope so he can't pinpoint anything.
Once the car warms up everything is fine. Like once the temp gauge reaches 3/8 or 1/2
Other potential symptoms and info?
- Starting idle a little rough (not terribly, but moreso than I'm used to). It also appears to have gotten rougher since I bought it in January.
- Started after I let the car sit in the driveway for 2 weeks while I was on a business trip. Odometer was stable, so I know nobody pulled a "Ferris Bueler" while I was gone.
- Rear diff was leaking about a month before it happened. Took it to dealer, they said they replaced a seal.
- 2,900-something miles
- 06 CTS purchases in January 06
- 3.6L V6, Auto trans, lux pkg, sport pkgIt. Stock everything.
- I've tried changing gas stations and using premium since it happened, no luck. Also tried running car to 1/8 and filling up with Premium from a good gas station (to burn off some "bad" gas). No luck either.
Obviously I'm not expecting a final answer, but I'd like to know some possibilities before going in. When it first happened I thought I had spun the tires but the roads were dry, the screen wasn't coming up, and I wasn't accelerating anywhere near as fast. And on later "experiments" on clean/dry pavement had friends check from outside car and said it wasn't spinning.
Need Help! Strange Behaviour on Cold Start - Like a Bucking Bronco 
