We're not sure what book you're referring to, but the instruction manual doesn't say anything about temperaures, that we could find.

Idling a model car engine for several tanks' worth of fuel is a sure way to shorten the useful life of your engine. The model must be run with the needles at a rich setting.

As far as teps go, we ignore them in tuning. Temps are unreliable. If the engine's running well, and is rich of peak RPM, then the temp you read is correct, no matter what anyone else says.