Engine surging during throttle advance. Governor inspection advised.

Q I’m experiencing engine surging unless I advance the throttle very slowly. During a surge, rpm varies from 2300 to 2500 and manifold pressure varies from 34 inches to 38 inches with throttle, prop, and mixture all full forward. The engine is low time (100 hours). We’ve replaced the wastegate, wastegate actuator, and turbo controller and the engine is still surging. The AH1A series engine uses a slope controller. If throttle is advanced very slowly, MP runs rock solid at 38 inches and the rpm is solid at 2500. Oil pressure, temperature, and TIT are all normal. Can anyone direct me where to start troubleshooting the problem or direct me to an expert to talk to? My highly experienced A&P is at a loss right now.

David Crass

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