I just had the dampner, tensioner, idler pulley, and serpentine belt replaced. Maybe it's my imagination, but it seems like the car does not idle as smooth as it did before fixing that stuff. It actually idles fairly well, but I once saw a '92 300d that was super quiet, I couldn't believe it, and very smooth at idle. What can I do to make my '91 300d quieter and smoother? It only has 90k miles on it. Engine mounts have been replaced previously.