how do I stop engine run on?

X-5 on the idle speed.

I have to run around 1000 rpm with my big cam and it tends to run on on shut down.

Sometimes my idle is lower depending on engine temp, load, and your typical Holley temperament and the idle is lower when I shut down, and it never runs on then.

With four speed cars you can pop it into gear and pop the clutch to snuff out the run on rotation to save yourself the embarrassment of feeling like your car is a clunker.