This just happened on my 1999 cherokee, 4.0 sport. Drove half hour, engine light went on in the last 5 minutes of the drive. As I sat parked in my driveway the engine was running as if my foot was on the gas lightly. O2 sensor? I hope it's not the computer as that went on my 1994 grand cherokee.

 

vacuum leak? not sure but dont think 02 controls idle speed. Dont quote me on that like i said not sure.

 

Computers don't go out as much as you would think. The best part is when the ce light comes on it stores a code in the computer. Take it to an auto parts store they will read it for you for free (discount auto parts, autozone, pepboys, etc) you will know exactly what went wrong.

 

Thanks everyone. It was a throttle sensor switch. Good as new now.