Edis 4

[Big Vern]

I shouldn't have thought it possible to have 'red' exhaust at idle unless you'e waving an acetylene torch on the exhaust! Simply not enough calorific value at idle to generate that amount of heat...
At full throttle or close too, then most of the heat is due to retarded ignition though some could be due to friction as the hot gases pass over sharp edges inside the exhaust.
Detonation forces ignition values retarded from optimum thus moving end of combustion closer to the opening of the exhaust valve and thus hotter exhaust temp. You can offset this by richening fuel mixture to cool combustion but this is at the expense of fuel ecomony.
A very lean mixture is unlikely to raise exhaust temp. significantly as the combustion gases become too diluted with excess oxygen reducing energy (heat release). Optimal fueling for something like a Zetec would be 13:1 AFR for full power and around 14.5:1 AFR for cruise/ idle. and about half an AFR richer at full power for a Pinto to allow for poorer fuel distribution across the cylinders.

HTH BV.