If you are too rich, it does cause high EGT's. its Afterburn, cuz the fuel/air charge is still burning as it exits the cylinder.

so sometimes, it can be hard to tell which is which... but if you are trying to tune solely by EGT's you are a fool and deserve to break something... especially if you ahve a DSM. DSM's, you have to tune by Ignition timing, then knock count, and then EGT's... but, EGT's are the same priority as WG O2 values... they have to be used together, cuz thats how you can tell if you are running high EGT due to excessive leanery or excessive richery...

if your car has knock-referenced ignition timing, you should be lookin at that. when the ECU sees all the parameters are acceptable, then itll advance timing. but, anyhow... thats mostly for cars w/ w/ ECU"s designed to run boost.