MOONEY 231 PLT HAD A MALFUNCTIONING INST VACUUM SYS THAT CAUSED PROBS WITH THE ATTITUDE INDICATOR AND HORIZ SIT INDICATOR.

Narrative

ON A FLT FROM SDL TO SMO; WE WERE APCHING THE PDZ VOR AND BOTH THE BACKUP ATTITUDE GYRO AND HSI WERE GIVING READINGS. WE HAD JUST EXPERIENCED SOME LIGHT CHOP. THE ATTITUDE GYRO SLOWLY SHOWED A 10 DEG NOSE DOWN AND 15 DEG TURN TO THE R. I WAS ALREADY TROUBLESHOOTING THE HSI THAT WAS SHOWING A HDG FLAG AND WAS NOT RESPONDING TO TURNS. I WAS TRACKING THE GPS AND ATTEMPTING TO DISREGARD THE OFF-LINE HSI AND THE NOW WAVERING ATTITUDE GYRO. IN ADDITION; I WAS DEALING WITH SEPARATION ISSUES WITH 2 ACFT THAT WERE GENERATING CONFLICT ALERTS ON THE GPS/S XPONDER LINK. BOTH ACFT WERE LESS THAN 1 MI AND LESS THAN 200 FT SEPARATION. WHILE DEALING WITH THE ABOVE ISSUES; THE AUTOPLT WAS STILL LINKED TO THE HSI AND THE ACFT DEVIATED FROM THE ASSIGNED COURSE. ATC GAVE US A VECTOR TO RETURN TO COURSE. I REQUESTED AN ADDITIONAL VECTOR FROM ATC BEFORE THE 2 GYRO FAILURES WERE ISOLATED AND PROPER NAV WAS RE-ESTABLISHED. AFTER LNDG AND EXAMINING THE HSI; IT WAS FOUND THAT THE PLUG ON THE BACK OF THE HSI WAS NOT PLUGGED IN ALL THE WAY. THE HSI WAS RECENTLY REMOVED FROM THE ACFT AND REINSTALLED. THE ATTITUDE GYRO WAS REMOVED AND SENT TO FBO FOR REPAIRS. THE ATTITUDE GYRO HAS HAD A HISTORY OF PROBS. THIS ACFT WAS OTS FOR THE PAST 4 MONTHS DUE TO A NEW ENG INSTALL. THIS WAS THE 4TH HR ON THE NEW ENG. AS UNLIKELY AS IT MAY APPEAR; BOTH GYROS WERE TAKEN OFF LINE BY SOME LIGHT CHOP DUE TO MECHANICAL AND HUMAN PROBS. THE HVY WORKLOAD SATURATED MY ABILITY TO STAY ON COURSE FOR A FEW MINS.