[jhv48]

Runs fine at speed, overheats at idle.

Two things:

1. Probably not, but feel radiator hoses at idle and see if they are hot. If not hot, replace thermostat.

3. Most likely, since car runs fine at speed, when air is being forced through the radiator, either you need a shroud to make your fan more effective, your fan is turning the wrong way, or your radiator and/or fan is too small.

My choice is the shroud, then the fan.