"PID Autotune failed! Temperature to high"

Hi all.
I recently replaced the hot end resistor on my RepRapPro Huxley with a new cartridge heater and nozzle. Afterwords I noticed that, in Pronterface, the hot end temperature tends to oscillate around the set temperature by a few degrees. I figured a PID Autotune would be in order, but when I run the commands, the temperature rises, overshoots (around 30C over), and says PID Autotune failed! Temperature to high. This is the same for all the temperatures I try.

>>>M301 P12.000 I2.200 D80.000 (RepRapPro's/Melzi Defaults)
SENDING:M301 P12.000 I2.200 D80.000 
ok p:12.000 i:2.200 d:80.000 w:125
>>> M303 S150 C8
SENDING:M303 S150 C8
PID Autotune start
PID Autotune failed! Temperature to high
>>> M303 S100 C8
SENDING:M303 S100 C8
PID Autotune start
PID Autotune failed! Temperature to high
>>> M303 S50 C8
SENDING:M303 S50 C8
PID Autotune start
PID Autotune failed! Temperature to high

I tired to manually fiddle around with the PID settings, but I still get the same result. Any ideas?

Doesn't the Huxley use a 19V PSU? Did you get a cartridge heater suitable for 19V?

I think you can reduce PID_MAX to stop it applying full power. Try halving the value to 128.

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I did get the 19v cartridge heater, I'm sure of that.

I doubt PID_Max would be the issue. When starting a print, the hot end heats up properly with no overshoot. Identical to the old wire wound resistor installed prior. The fluctuating temperature seen now however is new. It's only during the PID Autotune that the hot end overshoots.

After further inspection during a print I realized this is not as much of an issue as originally expected. (At least I dont think it is)

While printing at a set 205C the temperature drops al low as 200.6C and as high as 206.2C; I assume this is normal-ish. Due to the lack of anti-aliasing in Pronterface's temperature graph, I have mistook the three pixel jumps for significant temperature changes since the whole range of the graph is only about 80 pixels tall.

This still doesn't explain the glitchy PID Autotune. The printer seems fine nonetheless.