PLA woes

All posts I've seen seem to suggest that printing in PLA basically involves just printing at a lower temperature.  Unfortunately that has not been the case for me.

I've tried everything I can think of.  My current (weak?) theory is that  that there is leftover ABS(?) in the nozzle, and that's affecting the PLA.  So:

- Has anyone printed PLA with the stock (MG) hotend?
- If so, were you printing ABS before and, if yes, how did you make the switch?

Tried cleaning with guitar string, didn't find anything (string just came out from top).  Plus, if there is a partial clog, why don't I have any issues at all with ABS?  Perhaps ABS is not as soft, so the extruder can still push it through?  The only evidence of a partial clog is that, when I switch back to ABS, the nozzle occasionally squirts sideways for the first 600mm or so (extruding in air to, hopefully, flush nozzle).

[Scratching head...]

Generally, I've had all possible issues with PLA (nozzle temperature inconsistency, flow inconsistencies, partial clogs, jamming from the top, stripped filament, warping on overhangs, dry extrusion, blobbing, stringing, etc etc), and I think I've tried pretty much everything (temps from 170 to 190 -- with Matterhackers PLA, recommended 195 to 215 --, PID autotune each time, measured filament diameter with micrometer, did extrusion multiplier calibration, double-checked E-step calibration, bed leveling, tried various bed offsets, tried with nozzle fan and without, with enclosure and without, with heated bed and without, etc etc).  I'm pretty much running out of ideas.  The *only* thing that hasn't been a problem at all is getting PLA prints to stick to the bed, but everything else has mostly been a disaster.  With ABS I have no issues whatsoever (and much less warp than with PLA, which goes counter to what I read).  I've tried two different brands of PLA (Matterhackers and Makergeeks, both of which seem to be well-regarded), with the same results.

Here is a summary picture (full size):

If I remember correctly, the unenclosed PLA print was at 174C (182C first layer) and the enclosed ones were at 172C (again 182C first layer).  ABS is at 197C.  Note that gaps in extrusion are always after retractions (I tried lengths 2.5 - 3.2 mm and speeds 70, 75 and 80mm, but the gaps don't appear to follow a regular pattern?) -- except for the gaps due to clogging (filament softened too much inside the enclosure in that one).

Also, despite calibrating flow (all cylinder walls are 0.41-0.43mm, with target width of 0.42), I get inconsistent gaps in solid layers (full size):

[Pulling hair...]

I'm shelving PLA until I get my E3D, but if these images remind anyone of something they've seen before, please chime in.