I have a low idle on my ls430, I have codes p0420 and p0430 currently, but I don't feel like either would cause this condition, in pursuit of fixing it I have put in a new VVT-i solenoid, I've replaced a fuel damper, and I've put in a new PCV valve, all of which has not raised the idle, i cleaned the throttle body, and tried installing a different MAF as well, and still no change. The car vibrates when it has the low idle condition and it is distressing to drive the car like that.

 

just a thought - do check all of the rubber hose lines : pcv lines, and other rubber components. I know many of mine were dried and rock hard.... which could hide leaks.

Waiting to see what the others chime in with helpful ideas...

 

I've inspected most of them and I don't see any crscks but I agree it would probably be good practice to replace them anyways and see if it fixes the issue, they are very dry and brittle

 

Could always do the smoke test to find leaks.

 

P0420/P0430 are caused when the downstream O2 sensors detect too much oxygen in the exhaust after the CATs, normally due to cracks where the Y-pipe flange was welded.
That extra oxygen detected will lead to the engine not running optimally, and could well be the cause of your low idle.
The four O2 sensors are a vital part of the info fed to the ECU and that data is used to determine how much fuel is injected, fuel timing, and ignition timing.
Check your exhaust for leaks between the CAT and the downstream O2 sensor, and get that problem sorted (probably needs a new Y-pipe or gaskets) and see if that resolves the low idle.