[b3lha]

JDM cars have temperature sensors in the catalysts and a warning light for when they get too hot.

I thought catalyst overheating was normally due to unburnt fuel getting in there. ie. Misfiring or running much too rich. All the suggestions above sound plausible.

My suggestion is to get someone with a laptop and cable to log the ECU data and look for any abnormality in the sensor readings. eg. If the coolant temp says 0 when it's actually 70 C. Or the MAF reading 50g/s at idle. That way you don't waste time and money replacing things that might not be faulty.

If you're in the Uxbridge area any time soon, come to my place and we'll plug in my laptop and compare all the sensor reading between your car and mine.