A truck came into the repair shop with possible the slowest idle ever.1997 GMC Tahoe with a very slow idle. It seems the car engine stops moving, even turning backwards before firing the next cylinder. The cause of this was the distributor was installed two teeth behind (retarded) causing the combustion to ignite when the piston was already halfway through the power stroke. It produced just enough force to get the next piston to repeat the process. Male mechanics laugh at how truck engine idles so slow as if it is breathing heavily, then checks monitor to see the measurements of its strobing