SF340 flight crew experienced erratic uncommanded engine fluctuations; ran the appopriate procedure which resulted in securing the engine and an uneventful diversion.

Narrative

Climbing between 13;000 and 14;000 FT. The left engine Np started dropping from 1270 to around 600 RPM. While it was falling I checked the torque and ITT and they were falling along with the Np. At this point very large fluctuations began. I went back to the Np gauge and noted a little more than 600 RPM as it climbed back up to about 1000-1100 RPM. It dropped again and started trying to 'recover'. I called for the emergency action card for an erratic/uncommanded engine. There was no positive change after the card's items were completed. The major fluctuations had stopped; but the engine far from normal or stable. We stopped our climb at 14;000 FT. The Np was still fluctuating between around 600-850 RPM; and the torque and temp were going right with it. Next we ran the emergency/non-normal checklist for an erratic/uncommanded engine also to no avail. This led us to proceed to the engine shutdown checklist. While the First Officer was flipping to and beginning the shutdown checklist; I informed ATC and the Flight Attendant that we would have to shut an engine down and to standby. We were just over 15 NM west of ZZZ. We completed the checklist while I was contacting Dispatch. I told Dispatch what had happened and that we were in the process of shutting the left engine down. Due to our altitude the connection with dispatch was not very good and we lost contact after I let them know that we were shutting an engine down; but before we were able to establish ZZZ as the nearest suitable location for the diversion. I had already decided that ZZZ was the best alternative given proximity; runway length; emergency services available; and the fact that the passengers could more than likely get connections from there. I just wanted everyone to be on the same page. The First Officer proceeded with the shutdown without incident. We had 3 hours of fuel on board; and I made an announcement to the cabin letting them know that the shutdown was precautionary and that; while it is not normal; it was safe and trained for. We landed without incident; taxied to the commercial ramp and were met by a station manager who escorted the passengers into the terminal. Also; we stayed in contact with the Flight Attendant so she would be in the loop and knew how long the process would take and when we would be landing.At first we thought it was an HMU/torque motor problem; but it was a faulty front Np sensor that led to the problems; shutdown and emergency landing