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Engine misfires at 5700 rpm


Model: 911, Year:1986, Mileage:115000, Type of use:Both Street & Track
Chris, Recently the engine has developed a misfire under WOT at around 5700rpm (within the accuarcy of the tach) that feels similar to the rev limiter. At the track, this occured about 70% of the time running up in 2nd and 3rd gear. Other times it reved fine to red line, and to the acual limiter. This was the first hard running since an enlarged throttle body was installed this spring along with the extrude hone process on the intake manifold and the injectors cleaned and tested by a shop specializing in gas injectors. The air sensor flap had smooth travel all the way by hand when it was off. The CHT sensor was also replaced with the 2-wire one at the same time. Plugs, cap and rotor have 15-20,000 miles. Plug wires are likely original. Chip is presumably original. I intend to start diagnosis at the plugs and work back, then fuel if ignition looks fine. The engine otherwise runs well and pulls hard, except for a brief (30 sec) rough idle when started cold, and a intermittent hunting idle when hot, but these are not new.2 questions. Any ideas or advice on diagnosis? A previous answer in the archive (2001) askes if the air sensor flap valve opens fully at 5000 rpm. How can I check this?Thanks,Mike Nesbitt

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