If I don't let my car warm up long enough and I begin to drive it wants to quit

What is your question?

If I don't let my car warm up long enough and I begin to drive it wants to quit between 40 and 55 miles per hour, also during the day when I start driving right away it idles at 500 to 1000 rpms back and forth as I'm driving for a short time like the governing idle is messed up. What do you think is happening? Thanks for any advice

What makes this problem better or worse?

its worse when the engine is cold

How long has your 1990 Lexus LS400 had this problem?

for about 3mths