Flashing Lamp mopst commonly indicates a misfire, but also means something is out of wack that can cause damage to the CAT.....which could be the cause of all your issues. Check the PCV valve, check of induction leaks in the manifold area and check your plugs and plug wells for oil contamination.
The Thermostat on the L322 is both a conventional stat and also electrical....normally the stat works like a conventional stat, but if the ECU wants more cooling, it will heat the stat coil, forcing it to open further and aid cooling.
Sometimes, the wiring to the stat chaffs, or coolant begins to track up the loom and into the ECU. check for both.