What was found
(CAN) PRIOR TO STARTUP, PILOTS` FOUND THE LH MANIFOLD HEAT CONTROL JAMMED. FURTHER INVESTIGATION DISCOVERED ONE OF THE SCREWS SECURING THE AIR VALVE PLATE TO THE AIR VALVE SHAFT HAD DEPARTED, AND THE OTHER SCREWS WERE VERY LOOSE. WRONG TYPE OF NUT WAS USED ON THE SCREWS, CONTRIBUTING TO THE LOOSE HARDWARE. PARTS MANUAL REQUIRES AN365-832 TYPE NUTS, WHILE PRESSED STEEL TYPE OF NUT WAS FOUND INSTALLED IN BOTH AIRBOXES. VALVE WAS REPAIRED AND AIRCRAFT RETURNED TO SERVICE. THIS HAD THE POTENTIAL TO BE AN ENGINE FAILURE. (TC# 20061027004)