car runs fine but idles very rough at stops

Could be a vacuum leak, Idle Air Control Valve, spark plugs, bad/cheap gas (example: ARCO)... Things like that. I'd check all vacuum connections and hoses, since thats pretty easy/cheap to do... To locate the leak, get a can of carb cleaner. Have someone help you keep the car running while you squirt the car cleaner around the different vacuum hoses. When you spray a section of hose and hear the engine smooth out or the RPMs increase, that area is your problem. Keep squirting the area until you are able to locate the hose with the leak.

Should have trouble codes... Need to know what they are to prevent guessing at the cause!