MkIII Turbo missfire after heat soaking.

[professorbob]

Installed a loaner tri-coil pack yesterday. Thanks Tyler for allowing me to use the coil pack. The cold engine started with no skip. I drove the car hard for about an hour and the engine seemed to be building good power. On return to the garage, I noticed a slight pop at idle. I turned the engine off and let it heat soak for about 10 minutes. On start up the miss had returned. Thinking I may be having a precursor to a blow head gasket. A little You Tube researched indicated there is a test unit to check it. Rented the device and purchased some test solution. Tonight I drained some fluid from the radiator. inserted the appliance in the neck of the radiator and started the engine and let it warm up. The test reported negative for Hydro-carbon in the cooling system, as the fluid remained blue and did not change to yellow. During the test there was no miss present. After shutdown to replace coolant, and restart the skip had returned. Removal of the plug wires from each coil port did not appreciably change the sound. By the way, I was amazed and the distance the spark would jump in some cases three inches. So now I am trying to determine if I have an injector coil that may be failing because of heat. Or an injector with some sort of obstruction that is activated after heat soak. Any suggestions on how to check the injector. ( Not looking forward to trying to get to the units.).. Also, anyone have any other ideas about what could be causing the loss of power.