So we all know high intake temperatures are bad for many reasons, but what actually qualifies as 'high', and what is normal?
My latest project has been to fit a couple of temperature gauges to monitor the intake and manifold tempeatures (ie ambient at filter and post intercooler). I went for a roof mount setup, which I'm reasonably happy with the result.

I've yet to take it out, due to a couple of thing that need to be finished first. But I'm hoping to use it when I'm raising the boost, so I can see how well my setup deals with the extra heat load. Also plan to see what difference my water injecion setup makes.
 
But how much is too much when it comes to intake temps? When will it pull timing, and when am I risking detonation?
Stock ECU, CT20b, 98 octane.

It's a bit of a how long is a piece of string,as what many people find acceptable varys greatly.
 
Once you get to post intercooler/manifold temps over 60 degrees, its too hot.
40-50 is acceptable.
The problem with most factory knock control systems is that they only actually function in a fairly small part of the timing map, not everywhere like most people seem to think. I cannot vouch 100% for the MR2's system, but most factory ecus will have aggressive timing at mid to high load lower in the rev range (where the car is coming onto and peaking the boost) to register knock before switching over to the knock map. Generally speaking they don't have the ability to check knock up high, where heatsoak affects the intercooler, where a modified mr2 is likely to knock.

Is it a case of having two distinct maps, ie normal timing map and a retarded timing map that gets activated by knock? Or does it have some sort of progression?
I understand its fairly simple to tell when the ECU is playing it safe (TVIS not activated, turbo VSV closed, etc) so it could be a matter of wiring in an indicator light to monitor this. That would give me an idea of how the engine is responding to the heat.
 
I was seeing temps in the low 40s under moderate driving (ambient ~25) and it would creep into the 50s at idle, but that's not particularly worrisome as it dropped almost instantly with some airflow. The water injection definitely dropped temps, but its probably under-reading as the gauge is not far from the nozzle, and would be getting a bit of spray still.

most 90's ecus just have 2 distinct maps, and there is both a timing and fuel map, which are both triggered. another thing to keep in mind is pure water injection effectively lowers the octane rating of your air fuel mix, hence why there is usually water meth injection. hope this helps in some way, as I said I can't vouch 100% for Toyota. I can only go off what I know from Nissan and other mid 90's import ecus.

Are those the ebay temp modules?  Where/how did you mount the probes?  I want to do a similar thing to monitor the W2A water.
 
Cheers