Catalytic converter temp question?

The idle temperatures are not very meaningful.

The exhaust gas inside a catalytic converter is over 2,000ºF when running the motor hard. This is higher than when it left the cylinder.
The outside of the converter should never get over 1200ºF when a mechanic is in a position to measure it.
Ferrari F355 Exhaust unit sets its temperature alarm in the 1700ºF range.

 

I think it also triggers a CEL if there is a significant temperature different between the banks. I'm assuming your CELs and SDLs are working, Vinny?

 

I was wondering why you'd randomly test your exhaust temperatures. I thought you'd bought a new toy and wanted to test it out.

I don't think you could exclude a real engine/exhaust problem just because the light was intermittent. There could be an impending problem. You could try swapping the "converters" (Thermocouple TCUs) to see if the light switches banks.

(EDIT: I just discovered that your profile says you have a 1991 348TS... There are differences between 355s and 348s.)

 

Close to the same temperature,
variation at idle means the throttle bodies need adjustment:: 25º is ignorable.
variation at 100% throttle means the 02 sensors, fuel injectors, fuel pressure, headers, or ECU is not right.