Flight Crew Commercial; Flight Crew Flight Instructor
Aircraft Equipment Problem Less Severe
Flight Crew Overcame Equipment Problem
Aircraft
On initial descent for the approach; student powered back from cruise to 30%. When powering back; Instructor felt the aircraft starting to shake violently and continuously while descending. Instructor scanned engine instruments for any abnormality and noticed cylinder 4 EGT and CHT offline. Instructor; [as a] precaution; requested a visual for the south runway and switched the fuel tanks; turned the fuel pump on; etc. Instructor took controls. When nearing the airport; cylinder 4 came online; power was normal and vibrations ceased; abnormality was not duplicated throughout.
SR20 instructor pilot reported Number 4 cylinder went 'offline' on descent; but resumed normal operation shortly thereafter.