This month’s Ask a Tech feature focuses on a frustrating engine vibration problem on a Piper and an S-TEC autopilot issue on a Beechcraft. IA Mike Berry and avionics Repairman Larry Anglisano weigh in. First, an owner with a turbo Arrow chases a rough idling/stalling issue.
“The Continental engine on my turbo Arrow has a rough idle between 700 and 1100 RPM, and then smooths out nicely above 1200 RPM on the ground and in flight. It also has a (possibly unrelated) tendency to cut off at low RPM settings, but only after flight. Start it on the ramp, and it idles fine. When rolling out after landing, it will die if I don’t give it some throttle. Multiple mechanics have looked at the cutoff problem (checking idle settings and fuel pressures) and the only real solution was to increase the idle speed to 800 RPM. That, however, makes the rough idling issue even more pronounced. One mechanic has even suggested the rough idle was caused by a propeller balancing issue. I’m not so sure because it’s smooth at higher speeds.”