I'm having the same / a simular issue of temperature related readings, but at a different temperature level (for me it must be > 14 degree). I massure the dew point as well (temperature = orange, dew point = yellow). It looks to be more related to water in the air than only to temperature.
@zboblamont have you been finally been able to find a solution?
@mvader Turn the time delay adjustment preset on your PIR module to the minimum.. Now try it.. You will not get a continuous output..Also, prepare the circuit using a long wire from the back to the sensor of your module.
@tnick I know this is an old post, but if it helps you - I've created support for STM32 based on latest STM32duino here. It's currently made to be backward compatible for the existing STM32F1 support, which is what you are struggling. But with a small change you can use the new STM32 HAL support. Let me know if you are interested to give it a try.
The longer term plan is to remove the existing (old) STM32F1 support in favor of the new and more general STM32 support. (If @mfalkvidd agrees ;-))