twice last week when temps bottomed out at -20F, I had the following symptom
when I started up the following morning: the engine cranked, fired up, and
idled normally. However, when I engaged drive and pressed the accelerator to
go, the engine rpm did not advance beyond 2000. The accelerator pedal was
functional, but I could press it to the floor and engine rpm did not increase
the least little bit. This symptom persisted whether in D, R, or neutral. I
had just enough (2000) rpm to idle back in the garage. I let it idle for
10 minutes (closed garage door) where I suppose the temp got up to around 0
degrees. After 10 minutes idleing (warming up) in the garage, then the symptom
disappeared completely and everything was normal.

What's up with that ?

I had the _exact_ same problem a few times during the nasty cold snap in MN recently. The first couple of times, it just warmed up and was fine. The last time, it continued to not rev past 2K in -25F weather, even once it was warm. I discovered that by revving the engine (once warm), then dropping it back to idle repeatedly, I was able to up the RPMs by 100-200 each time. I did this until it looked like it was responding well enough and took off.

I drove through city streets at about 30-35mph without any problem, but when I hit the freeway after another 10 minutes, I found another limitation at 4000 RPM. I pulled off and repeated the revving until it cleared up and was able to jump to 6K without a problem. The weather has since warmed up in Minnesota and it hasn't reoccurred.

I have heard suggestions that the cold might be messing with a sensor which would be causing the computer to set a rev limit. No idea how valid that is. Any ideas?

I don't have an answer, but I would not suggest letting your car idle inside a closed garage for fear of Co2 poisoning. Many people die this way - even when they are inside their homes.

forgot to mention: a) detached garage, and b) driver was inside the house,
cussing out his candy-assed volvo, while his wife drove away in her 200,000
mile Toyota.