You are chasing a common symptom but looking in the wrong place.

The flashing led in the temp gauge has 2 meanings. It either means the
engine temp is seen as too high OR it means the coolant level is seen as
too low. If it happens as soon as you start then it can't be a hot
engine, so that leaves low coolant in the main tank.

Of course there are a few simple wiring problems that can cause the
symptom too, so some simple test steps can help narrow it down if the
coolant level isn't actually low. You have to check the main tank in the
engine compartment, NOT the one behind the license plate door. Then
check the 2 wire plug in the top of the main tank as that is where the
coolant level probes send their warning signal out.

Mark

Camins Bretts wrote:
> So, my 1983.5 1.9l WBX now has a wonky temp gauge AND the ECU indicator LED won't stop blinking no matter how long I wait for the ECU to self-check, or run the engine.
> Even if I:
>> Start the engine cold, or
>> Cycle the ECU by turning off the ignition and waiting, then wait with ignition on but not starting, or
>> Disconnect either water temp sensor, or both (cycling the ECU each variation), or
>> Disconnect, clean, and re-connect the ECU cable bundle.
>>
>> The 1.9l cold starts normally at ~ 1200-1400 rpm, and then drops the idle to ~ 800-1k rpm when warm, as usual. Engine seeks at hot idle a bit wider/faster than normally. Haven't been able to evaluate mpg.
>>
>> Suggestions, please? Thanks!
>> .
>>
>>
>