extruder extruding too much material (ABS)

I've just built a Prusa i3, and I'm having an issue with how much material is being extruded. I'm running Marlin firmware, and using Repetier Host with Slic3r. I've calibrated my printer, and it seems to function well, except I beileve it's extruding too much ABS. I printed the .5 mm thin wall object last night, and the wall thickness is about 1.5mm thick. I assume from the name that it should be .5 mm thick walls.

I've calibrated the extruder in the following manner:
1. Entered 650 steps/mm as a starting point in Marlin.
2. extrudered 100mm of ABS (with nozzle on, and running at temp (230 C) - is this correct?) This measurement is the amount of filament passing into extruder from the spool, not the length of .5mm that is being extruded from the nozzle.
3. Calculated the required steps/mm (using Prusa's v2 calculator)
4. ran several iterations, and arrived at 1003 steps (which seems high, but what do i know)
5. measured the actual diameter of filament, and entered this along with nozzle size into Slic3r.

When I try to print an overhanging object (I'm trying to print some ball and socket joints) the overhanging layers look terrible, and the nozzle ends up below the highest level of plastic, and ends up mushing everything around in circles, ruining the print. It looks like too much is being extruded, but what to do? Steps seem correct, if my method is correct.

Thanks in advance.
Atman

The cube wall thickness isn't necessarily .5 mil. You need to look at what extrusion width your slicer is putting out given your settings. In slic3r it is in the first few lines of gcode. That's what you should compare to your actual printed width.

Also, I've seen the same mushing when the extruder temp is too high or the print speed is too fast for the size of the object. The previous layer doesn't have time to cool and it all ends up a mushy mess.

If you post more details about your settings folks may have more useful suggestions.