found a couple things, not sure how helpful any of them will be to you:
[causes of high egt] In no particular order,
1 incorrect fuelling for load point (poor mapping)
2 incorrect ignition timing both too advanced and retarded can cause det, and high EGTs (poor mapping)
3 incorrect cooling both charge and high water temps.
4 bad cam timing.
5 restricted exhaust.
6 wrong octane fuel.
7 too much boost.
Thats all i can think of at the moment.
ok i see there are a few people that still have questions about does a rich mixture cause HIGH EGT's well here are some answers.
In a very rich condition the exhaust gasses will be lower do to a number of factors. The biggest reason and most obvious will be the lack of air to complete the combustion process. The Flame front created by the Spark will simply die out...thus lower EGT's. Now also another point is the Fuel its self acts as a "heat mop" (Takes away energy as it evaporates) and pulls away heat from the combustion area. Plus the remaining CO (carbon monoxide) from a rich envionment effects this process as well, it will convert to CO2 and again lower EGT temps.
Now in a Lean Envionment there is more air (oxygen being the primary Oxidizer) to sustain the complete combustion process..thus causing temps to rise and peak. This complete burn of both fuel and its oxidizer will give you the highest EGT's (peak) but here within lies the problem...too much heat from long pulls might cause "pre-ignition" (combustion (normal burn) before the spark occurs..not to be confused with detonation (violent burn))..pre-ignition is caused by a hot surface (valve,cyc..ect)..Indication of this can be seen in high EGT's. Now the environment is just right for Detonation..high combustion chamber temps with air and fuel being compressed causes the Event known as Detonation...the rapid and violent burn of the fuel/air mixture. The flame front during this Event travels 5 to 25 times faster then the normal flame front and actually disrupts the normal air flow going out through the exhaust. You will actually see a slight decrease in EGT's during "Detonation" plus you will hear it and such.
so basicly higher EGT's temps cause "pre-ignition" which could cause "Detonation". so if this was your car would you be conserned about high EGT's. I will leave that up to you.
You might have better luck in the engine management section.
They [jdm ECUs] need to be tuned. They run both a lot of timing and a lot of boost. I'm temporarily running an AccessECU stage 2 map on my V7, but using the STi boost mapping. Even with the detuned fuel and timing maps, the ECU wants to run too much boost for 91 octane.