Merkfan

hello everyone. I have a problem that occurs randomly and diagnostics is not detecting it. when it happens act like this: on start temp rises but fluctuate, sometimes it goes to 90ish stays there but sometimes goes to off(40deg) and momentarily back. if it fluctuate for some time car becomes jerky and/or if I stop it shuts down most of the time restart and drive on like nothing happen but problem comes back sometimes months later. car is now in a shop, suggested moisture maybe causing corrosion on connector and behaviour described above. what do you guys think? these problems are always hard to diagnose. any dr. House out there? much appriciated