Yeah well they do wear out. Mines hitting between 80 and 90. I can grab the belts and turn the engine by hand but it gets great mpg and I might drive it from now on.
It has been experience that when a cylinder hits south of 90 that it will not produce power. After the rpm is increased and the piston speed increases it will fire. But at an Idle? I use a MINIMUM of 110 before I give it her last rights.