I'm thinking a vacuum leak that seals up once the engine warms up......
Very true. Get some carb cleaner and spray around intake and other mating surfaces and listen for idle fluctuations. Do it when its cold though. If you have a hand held scan tool that reads data you can also watch the O2S voltage for fluctuations
![Driving :driving:](https://board.marlincrawler.com/Smileys/marlin/driving.gif)