John, I've had this problem recently too, so I replaced the pollen filter,(easy Job on an LS). One thing I've found though, and this applies to any car; I never use the Recirculation button without the A/C being on, because when it is raining, being in Recirculation mode without A/C switched on will guarantee you a quickly fogged up windscreen. Recirculation mode is only safe when it's not humid outside or it's not raining. In fact I found that the A/C works better with Recirculation switched on. Having only outside air to the vents i.e. Recirculation off, also stops fogging up.