cool (one's) jets
1. To calm oneself down; to become less agitated. I was really angry, so I had to just take a second and cool my jets before I did anything rash. Cool your jets back there, we'll be home in a few minutes.
2. To stifle or control one's eagerness, enthusiasm, or hastiness. The young senator has massive support in his home state, but he'd better cool his jets if he thinks the rest of the country will consider him presidential material. I know you want to get this project over and done with, but cool your jets and do the work carefully.