Numerous posts have been made by myself and many others regarding a problem idling when really cold ( 20 f) or lower. I and many others have done a number of the usual things like changing intake manifold gaskets, checking for vacuum leaks, tune ups, pvc hoses but to no avail. The car starts normally, fast idles for thirty seconds and then drops off to hot idle speed around 500 rpms which is not enough to run smoothly when cold and then the check engine light and sometimes misfires ( blinking CEL lights)(.

I discovered that if you cold start the car and let it run rough for a 40 to 60 seconds then shut the car off and restart it. The second time around it will run perfectly?

 

Here is a check list to try:

jaghelp.com: That pesky rough idle

then when you are done doing all these it will be a good idea to disconnect the battery before you go to sleep and reconnect it in the morning.

If all that doesn't work it might be time for new spark plugs and coils. Best of luck!