If its running rough it could have a failed intake runner flap, or bad engine mounts.
It should be smooth. Just did the repair on mine -- You can see the broken plastic in the center.
At 170k I would replace the entire manifold due to the plastic inside if that is the problem -- so thats $550 in parts at best (wont always show CEL! needs to be scanned by MB or good scanner).
Balance shaft is a lot more and requires engine out, so priority #1 would be verify if its been done. If its within the engine range and has not been done, I would walk.