Running a lot of fuel cleaner isn't good for your spark plugs, just saying. If your exhaust is blowing out hot then that means you don't have any intake valves too tight.

 

The fact that you stated you had tight valves in the past really leads me to believe we have a burned valve situation as I had stated earlier. A leak down test is in order. A slightly burnt valve will only get worse over time, not better, no matter how much injector cleaner and fuel system treatment you dump in.

 

By "a couple of tight valves" he meant that they were in spec, just on the tighter side - nothing that he said would cause damage. He said everything checked out.

I'll go the route and buy a compressor to do a leak down test if you think it's worthwhile.

 

Was this issue ever resolved?

 

I had a mystery misfire, for yrs, replaced so many parts, tried different oils, so many spark plugs/coils/sensors.... Until I finally decided to swap the ecu, and finally found the problem, the ecu went bad somehow, and it only cost me 175 to fix, I was so relieved after yrs of hunting and guessing.