[toc]

If you have a Manual Transmission, shift into neutral and the RPMs increase (i.e. from 700 to 1100) - what is the likely cause?
Vehicle motion causing more air entry and therefore raising the required RPM or...
The car moving giving a signal that it needs to maintain a higher idle for some reason?

The testing I've done suggest that as the car slows, the RPMs drop back down - but above say 40 or so, the RPMs rise as if there is some reason to maintain a higher RPM.