92 Probe running rough

I have a 92 Probe w/ 4 cyl turbo. It was running excellent until some guy came over to look at it (I have it listed for sale). It was idling fine, then he pulled off one of the plug wires from the dist cap. There was a loud pop, and now it is running terribly. Idles rough, and cant get much power.

Any suggestions would be great!

Thank you