Today I had to do a -28C cold start on the Bonneville. She turned over a little slow, but started quickly none the less. It then ran at about 1500RPM'*, but for the first 30 seconds or so it was making a stumbling sound every couple of seconds...it was quite noticeable and I had never heard it before. Then it smoothed out completely. I hope it was a one time thing.

could be the computer relearning the idle? my 92 SSESC always kinda has a icky idle after the battery is really low, or is disconnected. goes away after idle falls back down to 700 and doesnt come back. just keep a eye out for it happening again.. and be glad your bonneville is starting in that cold. :P

If it was damp out it could have been a little moisture on a wire or plug.

Could be simply cold enough for a wire or plug to show an issue. Once it heated up it was all set right?

at -28-32 degrees, you'd be REALLY lucky if the car starts without being plugged in.

Get a block heater, or plug it in, if it has one.

I remember when I used to drive a sunfire last winter, when my buick tossed the rod, the coldest day in winter, the car would barly start, just crank over slow, really slow. When i plugged her in, it solved the problem there.

It has a block heater, I just hadn't planned on going out. And yes, once it was warmed up in was just fine. It hasn't happened since.

I wouldnt suggest plugging your car in, I started plugging mine in cold weather only to realize that the car gets used to it, and when I was somewhere where I couldnt plug it in the car for the night, even if it was -15 it wouldnt start, the best thing to do, know it sounds stupid, is to put an old blanket over your engine to block the cold wind, my grandfather used to do this when he worked for gm. and I remember it being -35 and he had no trouble firing it up.