Inconsistent extruder

Hey folks, my extruder is making me crazy and I'm hoping someone can help.

I have a RepRap prusa-mendel i2 which was working pretty great up until recently.

My prints are currently not working at all. The filament is extruding, but the hotend is picking up the starting layer as it prints, leading to a gummed up mess. Amazingly, that's not even the problem I need help with. I thought maybe my extruder calibration was off so that might help. Well, it is indeed off, but I'm having a heck of a time trying to fix it.

So, I hit extrude 20mm and 14mm came out. So I recalculated my steps, updated firmware, tried again. I hit extrude 20mm and 8 came out. Without changing anything I hit extrude 20mm and 24 came out.

I have restarted, tried other values, tried hotter and cooler, and I'm going crazy. Nothing gives a consistent extrude value!

Any ideas? TIA!

Inconsistent extrusion is a pretty clear indicator of either missing steps or the filament not being gripped tight enough by the extruder. Extrude 100mm of filament and watch the extruder gears closely. If they hesitate at all, you've got missing steps due to either overheating or incorrect vref on the stepper driver. If you're not skipping, then the hobbed bolt is probably not gripping the filament tightly enough.

Check the reprap wiki for vref instructions. Overheating can also be caused by incorrect vref.

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Do you clean the hobbed bolt regularly?
Ive got a little wire brush and a compressed air canister to clean mine.

Gordon