Try searching 300E's and 'Engine Harness'.

You will see a myraid of problems that are associated to the "Witch Hunt" you are experiencing. The harness was poorly designed and breaks down almost completely leaving cracked, dried out insulation exposing bare wires to the whims of Mother Nature. The harness plugs into the engine control box in the passenger side of the engine compartment behind the battery beside the OVP that you replaced. The other end feeds through to the various sensors around the back of the head and up to the front of the engine above the intake manifold.

I hope this will help you find your problem and I will monitor this post to watch your adventure.

Did the "coil" suggestion help? Faulty coil(s) certainly do breakdown at different temperatures.