The injector pop tests revealed that all are still at 2000 psi with a very good spray pattern, just as they were when I rebuilt them about 6 months ago.

But... the compression test revealed that the number 4 cylinder is too low, ie 210 psi, where all the others were 340 or above. Just to be sure, I double checked the valve lash on that cylinder and it was spot on.

This engine does not burn any oil, the blow by is normal or better than normal, there is no residual pressure in the radiator coolant reservoir in the morning, nor any smell or oil in the engine coolant. The valves on the #4 cylinder do not stick when observed with the valve cover off and while cranking the starter.

The good news is that I have a good idea what is causing the engine lope at idle, but the bad news is that I have to remove the cylinder head to find out exactly what is wrong. Not happy right now