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Plug Not Tightened After Oil Change

Add to that compression tests are difficult to do and get accurate results. If those readings are correct I concur w/the advise above it is time to check the valve clearances. OP, doesn’t your owner’s manual suggest a routine valve clearance measurement/adjustment every so many thousand miles or so many months? On my Corolla I think the manual recommends valve clearances be measured at least every 30,000 miles.

To add to my prior comments about the dealer and lack of or not really caring about the compression.

  1. There is an obvious issue. They should have done a wet test at that time with the plugs out.
  2. They either assume those readings are fine because they’re ignorant or they’re aware and trying to BS their way through a dicey situation.
  3. Yes, low compression can be due to incorrect valve lash. This is also something that would easily show up on a wet compression test and is certainly something these guys should have factored in.

Additional: If there is a lash issue and it involves an exhaust valve there is a good chance that any improvement after properly adjusting the valves will be short-lived. Exhaust valves can be damaged in only a few miles if the lash is too tight. Eventually that near microscopic pitting or rutting will increase over some unknown number of miles, lead to a misfire, and then the only cure is a valve job or cylinder head replacement; depending upon severity of the damage.

Best of luck.

@GeorgeSanJose has good advice here. Thanks for the idea for a BestRide story!