Any armchair quarterback has — long before this point — figured out what went wrong: It was the fuel servo that replaces the carburetor in a fuel-injected system. It has a butterfly valve to control the air entering the cylinders, linked to a fuel-metering valve, and both are connected to an external arm to which the throttle cable attaches. The one I had located, purchased and installed had all the same letters, numbers and dashes as called for in the plans, except for the very last digit, which was one different. Externally, the unit looked identical to the proper one: same bolt-hole size and pattern, same fuel port locations and thread sizes, same throttle and mixture arm location. The only difference was that the butterfly valve inside the unit was mounted 90 degrees off from the correct unit. This meant the valves were fully open when the throttle in the cockpit was fully closed. Had I been actually seeing and understanding what I was looking at, I would have realized that the unit does not have an adjustable full-throttle stop for the external arm that is the idle-speed adjustment.