Rough Idle or engine loping at idle. HELP!

Just in the past day or so I have noticed my 01 Jetta tdi idle roughly or lope while idling. It only occurs while idling and is intermittent. Their is no power loss being experienced nor an engine code coming up. The only difference is I have done a 50/50 mix of diesel #2 and biodiesel and I do have 176000 miles. The fuel filter has been changed 5000 miles ago and it is the first time the car has run on any amount of biodiesel. I just can't figure out why it would be sputtering or loping.... HELP!

BioD has excellent cleaning properties. Wanna bet it's cleaned the fuel tank, injection pump, and fuel lines? Change the filter and see if it solves your problem.