The point is that the valves aren't tightenable, they are hydraulic. Whatever they didn't accomplish can only be determined by evaluating what your condition is and maybe from that what it was.

The likely candidate is a collapsed lifter and is really not much more expensive to fix than your car cost. But it could be a worn cam which is a little pricey. If it is a lifter and it doesn't get fixed it will wind up needing a cam.

Someone who will know what to look for will have to take a look.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician