Yes, at idle the airflow gets cut off, and this affects the airflow that cools the radiator at higher speeds.

When the cooling system is inefficient (a lot of factors - coolant flow, coolant/antifreeze mix, faulty fan switches,etc), this results in your running temp going up.

When you talk about shifting to neutral and revving it, this refers to the clutch fan.

Doesn't your aux fan also cut in when the temps go up?

The proper operation of these 2 fans, coupled with an efficient cooling system should keep your running temps around 100 deg, at most, even in a jam.

As an example, my kid brother's 190e (same model as mine but 1990) was stuck in a 2 hour jam returning from a F1 race.

He monitored his running temp at no higher than 95 at all times, with both fans cutting in and out with the temperature changes.

The outside temperature was 34 deg Celcius!Go figure!

Have you serviced your cooling system recently?You know the drill - flushing, test temp switches, check thermostat, etc.

Cheers.