Look on the injector mounts. Each is held onto the head by a single cap screw. On both ends of the cap screw there should be an insulating washer (some sort of phenolic material) -- one between the mount and the head, another between the mount and the screw cap.

Those are to keep the injectors from getting hot enough that fuel vaporizes in the injectors instead of atomizing when sprayed out. Symptoms are difficult hot starts, and dropping idle on a hot motor.

If those insulators are missing on yours, you'll need to replace the O-rings under the mounts when you correct this, as they will have been overcompressed.