Random layer under extrusion

After assembling the kit I have had some good prints, great prints, but totally random under extruded layers. I have watched the nozzle temp fluctuate +/- 3-5 C, but I'm printing PLA @212C so that should not cause jamming or under extrusion via temp. I'm also not hearing extruder gear slipping or clicking sounds. While watching and listening, everything sounds completely fine and normal mechanically, but I can see the extrusion start to create gaps all over the place and turn an otherwise beautiful print into a holy sponge. I've had prints run for 2 hours and they come out perfect, overnight prints run perfectly for 6 hours and the final 5-10 layers turn to crap, then a 30 minute print has random problems in the first 5 layers and recovers for half the print and then starts acting up again near the top! It is NOT the filament, I know this because I have used lots of it in TWO other printers and have never had this issue. I've run this filament through a cheap Wanhao i3 clone with a Micro Swiss hot end and had amazing prints. Also note that the prints I'm talking about getting screwed up are direct gcode from Prusa and not my own slicing AND those that I have sliced myself.

Extruder tension screws are at 12mm. All belts are tight, not that they'd have anything to do with underextrusion, screws tight everywhere, etc. I have yet to do a PID tune, but I cannot think of a reason that a 5C fluctuation would matter on PLA when I'm set to print @212C as this stuff still pushes out fairly well down to 200C.

I'm about to pull out my hair!

Answer this question I have this problem too

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I think that gap on first layer are from Z ajust, so the nozzle need to be closer to the bed (0.1mm can change everything).

If you want to manage these parameters, then edit the configuration of slicer software and play with things like "first layer height", "first layer speed modifier" and "first layer extrusion width".

Same with solid end top layer parameter. But you'll need a lot of test to find the right parameters that do "what you expect"... Be brave :)

PS : i hope english is you mother tongue because it's not mine and slicer parameters fine tune was an huge experience for me \o/

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