Alleviated the problem on Sunday morning, after removing the hose from the Header Tank to the Water Jacket of the Turbocharger, as I was replacing it with a silicone jobbie. Turned out to be that the plug connecting to the physical temp sensor was hanging loose, hence why I was getting these errors.

Just took it for a bit of a boot then, CEL popped up, switched it over to diagnostics mode and it's popping out 21, 22 + 23, as it did last time.

I don't know why 22 (knock sensor circuit)and 23 (AFM) are attributed with this, if anyone could explain it would be good - because as soon as CEL Code 21 is lifted, they fuck off too. I presume they're on the same circuit.

I'm sure the plug has just wiggled off again, so I'll have to wait til the engine's cooled down, turkey baster the header tank, remove the silicone, so I can get my fingers to the bastard of a thing again, and rectify it - hopefully this time for good. I'm sick of the car running stupidly rich in the mornings when this error occurs, as it's a bitch to start

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03 STi @ 280hp/1.3bar

I had the same problem, turned out to be the connection to the ecu...
might be worth checking.

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Straya

Already alleviated, plug was loose

I'm pretty sure the AFM and Knock Sensor belong to the same circuit, as soon as the Coolant Temp Sensor goes, all three go.

Mods, close, don't delete - keep this thread as a point of reference to people whom may as well come across similair issues.

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03 STi @ 280hp/1.3bar