Now that was unexpected. I took off from a traffic light more briskly than usual (about half throttle), and when I let up on the accelerator the car continued accelerating. I started braking and fortunately the engine started missing and I was able to pull into a parking lot. After shutting the beast down I started the engine and it appeared to be at full throttle - banging the rev limiter repeatedly. I checked the throttle position on the TB and it was hard against the idle stop. I tried restarting a few times, including starting the engine with the accelerator fully depressed. The dash readout was flashing Traction Control/ASC Not Available, or something similar. On about the forth or fifth startup attempt the engine started and ran normally. The CEL was on at this point, and I had a P1229 code - Electronic Throttle Control Circuit. I did have the throttle body off while chasing some vacuum leaks a month or so back, but the beast had been running flawlessly since. The problem has not repeated during a few local trips, but obviously I'm concerned that it will return. Thoughts on what to look for or action to take will be appreciated.

 

I had a similar experience in a '69 SS Camaro and it turned out to be a frayed throttle cable.
It would only stick if you hit the pedal hard, otherwise no symptoms. My only solution was to
turn the ignition off.

 

My first thought would be the TB with the code it's thrown. I can imagine the event was scary so I hope you're okay!

The TRAC flash with be related to the battery, cycling starts can deplete it quickly so I doubt there's an issue there, but how old is it?

Have a good look at the induction for major air leaks.

Play with the throttle, engine off. Look at the signal from the TPPS via an obd reader and look for smooth percentage rise and fall with pedal pressure.
You're looking for any stops, stumbles or oddness.

It sounds like the throttle plate is sticking, maybe a new cable, a cleanup or new throttle body sensor. With any of that a hard reset is good form after tweaks.

 

Unfortunately I can't find a TBPS function in the live data menu on my code reader - should I be looking for something else? The mechanical linkages are fine, and the TB was just cleaned when it was out chasing vacuum leaks. Fuel trims are now +- low single digits. The battery is fine, and the multiple start attempts didn't involve much cranking - the beast fired instantly each time, but I had to shut down due to the uncontrolled acceleration. I've driven a few more times including some full throttle runs and everything is working fine. It's disconcerting wondering if the problem will resurface. Any additional thoughts welcome.

 

When this issue occurred, had you been driving for quite a long distance and/or time? Stop and go or just highway?

 

Local streets - some stop and go - for about 5 minutes or so.