Hi there my 740 gl was idling rough so I replaced the Idle air control valve. The car runs much better now (doesn't think about stalling out at red lights) but it still idles rough in drive. If I switch to neutral or park the roughness is not noticeable. Any pointers or tips are greatly appreciated.

 

you might clean the throttle body. inspect all the vacuum and intake hoses.

 

Do you may be have an engine misfire? Pull the plugs' wires one by one using some rubber insulating device to avoid shocking yourself to see if anything changes (it should). If no change, the plug pulled is the are you should look at: could be the plug, the wire, even the injector.

Or the idle speed may be too low. What does the tach say?