Anyone else get p0420 ONLY in winter?

[Y2KSR5]

In the winter it comes on ever 100-200 miles after I clear it. As soon as 50* plus weather arrives the code does not come back? Of cousre Toyota told me I need a $1200 cat without even looking under the vehicle. Why would the code only show up in the winter?

 

[99yota4]

Oddly enough, I think I fall in that category. After resetting my CEL (P0420) a few weeks ago, it hasn't come back and I drive alot. Weather has been relatively warmer but there has been some cold nights. I wonder what could be the cause of that

 

[TheDurk]

When my rear O₂ went bad, I was able to clear it all summer and fall and get another month or two without a code. Then, when it got cold, it came back more quickly until it was in the 100 mile/half-a-tank mode. I finally changed it in Feb. '09 (March was inspection month) and have not seen a P0420 since. I have no idea if there is a cause involved here or just coincidence.

Slightly OT--this winter I had a high idle, around 1050. I don't spend much time at idle so I was waiting for warm weather to get out there and troubleshoot it. As soon as the weather warmed up, the problem went away. Now I have to wait until next winter, I guess.