You can adjust the "flow" (a technique pointed out to me by R Design ) by going to the Tune menu, only visible when printing and altering the flow rate of the filament to see if this makes a difference. I had calibrated the filament using the 100 mm technique and this was just about spot on, but I still had lip like lifts on the first layer and on the last layer and in general the nozzle was pushing a blob of filament along which eventually detached and stuck to the print. I tried adjusting retraction etc. with varying results but adjusting the flow option during a print and waiting for a few layers to be printed resulted in the effect going away and the print looking good again. I then used the extrusion multiplier found in s3d, Edit Process Settings, Extruder tab, to get the same effect, the result was like magic, perfect layers again, no blobs, zits, or lifting. This may not be your specific problem but it's useful to know that some things can be adjusted on the fly from the front panel. I have yet to see any documentation on the Rumba front panel menus, but this must exist somewhere.
I changed the extrusion multiplier to 0.94 from 1.0 having said that I still need to tweak the "flow" but I guess it because I have ABS sitting on the back of the printer for a couple of months and it seems it absorbs moisture from the atmosphere.
