I just changed the spark plugs in my 1997 Impreza Outback Sport, and now it wont stay running. When I start it, it starts right up, settles into a nice smooth idle, runs for exactly 7 seconds, then stops running. I have tried it multiple time, one right after the other, and it does exactly the same thing. in order to get to the rear plugs, i unlatched the air cleaner box and pushed it up and off to the side, & I also took off the windshield washer reservoir and pulled it forward. I didn't disconnect any wires. Does anyone have any idea what may be going on here? Is it possible something got disconnected that I can't see just by a casual inspection, or just looking at it from the top of the motor? I thought that maybe I might have to reset the computer or something, so I unhook the battery waited for a few seconds, and then hooked back up. But it still does the same thing. No engine check lights or anything else coming up that looks out of the ordinary.

100% it is an air intake air leak. Most likely one of the many smaller hoses is still disconnected. 

What he said. Make sure all of the hoses are connected properly to the intake tube.

If it has the big box at the back make sure the bottom of the box is clipped together properly.

100% it is an air intake air leak. Most likely one of the many smaller hoses is still disconnected. 

Thank you John. You were 100%

correct. I just went out and unhooked the airbox again and when I lifted

it up, I noticed that the largest breather hose had popped off.

I put it back on and it stays running now.

Thanks again.