Looking for input, attempting to adjust the buffer screw on a 8V71 that has fast idle & buffer switch for Jakes. After a few attempts to have the fast idle work but couldn’t get the Jakes to shut off at idle, only at fuel off, would the buffer switch activate. Then it happened, the next start RUN AWAY, pushed the emergency stop, nothing, ran to the back manual trip flapper, guessing 3000 RPM by that time. When the flapper engaged, it slowed the engine down to around idle (with lots of black smoke) but would not shut down. Ended up unscrewing the fuel filters, finally slowly the engine can to a stop. Today reprimed back off buffer screw (to be safe) and she firered up normally. Still can’t get the Jake buffer switch to engage at idle. I have all the books, GM manual, Detroit service manual, and Jacobs instruction manual, am I missing something, says tighten buffer screw to no more than 15 RPM increase, I stopped at 10 RPM increase. So why did the emergence stop not work, well the solenoid was bad. In 10 plus years with this coach, I never thought about checking that solenoid. And why did I have run away? The injectors were not stuck, the engine is not weak (inframe around 15 years ago, low mileage).