You didn't mention how old the power venter was. I would say you need to clean the pipe and blow out the PV every month or twe for heavy use and every three or four under light use. Also the special oil is needed to properly lube the motor. If you don't have our instructions for cleaning the PV, send me a PM with your Email and I'll send them to you. We will post them on the website by next week or so.
As Dave said you may not be pulling enough draft and the condition could be not related to maint at all. You need to adjust the rheostat up untill the baro opens (make sure the weight is on the correct scale, left side for horiz install and right for vert) with the weight set to the 4 on the scale, then back it off til it just flutters, that is where it should run 24/7. Over time you will notice it wil stop fluttering so you need to adjust it up to make sure you have enough draft.
Let us know how what is going on, a malfunctioning PV is not anything to take lightly and should be corrected immediately. Please also make sure you have at least two CO detectors in servicable condition monitoring the home.