84k LT1 in 1995 Buick vibrates at idle in gear. It sits quite a bit. However it doesn't run rough under any acceleration when it does get used. Really doesn't affect the way it drives so I don't think it's a traditional misfire. No codes have been stored at all since it started. When the AC is on the vibration is more intense and then goes away when the car moves, yet the baseline vibration is still noticeable when the engine is back at idle speed, AC on or off. Am I looking at some kind of a harmonic imbalance? Maybe a pulley out of round?