Timing chain on Chevy Corsica

Chevy Corsica, 1996; 200, 00 miles; 4 cyl.

A few weeks ago, I had to have the timing chain replaced. The car was running fine up until this time. Since it has been replaced, my car is running rough. It idles rough, uses excessive gas, tries to die at stops. I was wondering if you could tell me what might be causing it to run like this after having the timing chain replaced.

Thanks.