rough start

When I first start mycaprice in the morning or at anytime it idles very bad. Almsot like it has a large cam in it. It the 4.3 v6, but after a few seconds the engine light comes on and itsmooths out. What do you think it could be? I also have no reverse. I have the 200 metric trans. Its also shimmys sometimewhen you sow down to stop. what could be this problem?

I have the 200 metric trans. There's you're problem!
Just kidding, but the rough idle could be a vacuum leak, bad 02 sensor, bad EGR valve or EGR control, etc. Check the engine codes and that will help better diagnose the problem.