No option for year of my truck. Which is an 87 gmc Jimmy full size. 5.7 4x4. Tbi

What is your question?

Wen warming up the truck, every time, morning, afternoon and night, the idle goes up and down for about 5 minute or till warm up. It doesn't have trouble starting and runs great after warm up. No codes or check engine light on. Please help. Any advise or info would b greatly appreciated. Thank u.