CRJ-200 flight crew experienced fluctuating oil pressure at FL360 with pressure excursions below limits. When engine was idled pressure remained within limits but crew elects to divert to nearby alternate as destination had weather issues.

Narrative

While at cruise we received a triple chime; the aural warning; and the EICAS message for Engine oil pressure. The right hand engine oil pressure was fluctuating down to 20 psi (in the red) and back up to 35 psi (in the green). As the pressure went down the alarm would sound for about 10 seconds; then go out as the pressure returned for about 10 seconds. The engine oil temp and engine vibrations were normal. I called for QRH for Engine Oil Pressure and complied with the instructions. After we idled the engine the warning went away and stayed away until we tried to advance the throttle again; then it would come back the same as before. We decided to leave the engine at idle and divert. We complied with the QRH procedures for single engine approach and landing; leaving the engine at idle. We called Dispatch and informed them of our intentions to divert. According to our factored and demonstrated landing distances and the single engine factors; they had more than enough runway; an ILS approach into the wind; Airport Rescue and Fire; and they were right below us. The decision to divert was also factored by the fact that we had been told to expect holding in the next sector. Dispatch agreed with our decision to divert. We diverted safely and without further incident.