Unstable Extruder Temp

Very unstable extruder temp, happens only when heating, only sometimes when cooling down but never during a print when the temp is constant.
This started about a month ago but only happened every 10 prints or so.

I tried PID tuning ,different thermistor pin and recrimped the connector.
this also cause a "Heater extruder not heating at expected rate"
Using a Revo hotend.