My 1999 Rx300 recently began stalling when idling and the engine light came on- once I'm at highway speed it seems to run ok but as soon as I stop it dies as I have to keep my foot on the gas to keep it from dying-the error code PO420 indicates the catalytic converter is bad and needs to be replace. does the car dying at idle have anything to do with this error code and could a bad converter cause this? any ideas on this problem? Thanks!

 

It does come up as a cat converter code but its often times the oxygen sensors that are the problem. The failing oxygen sensor tricks the car into thinking the cats aren't doing their job.

Which bank was the code for? Bank 1 or bank 2?

 

Welcome to the Club

It's extremely rare, but a plugged catalytic converter could do this, but I seriously doubt it as you would not be starting up the vehicle at all or very little.

It sounds to me more like you may need to clean the IACV valve, https://www.clublexus.com/forums/rx-...-write-up.html

That's usually one of the main culprits for causing the vehicle to shut off at idle. I am thinking the P0420 is showing up as the vehicle is not getting enough air, causing a mismatch in the air/fuel ratio causing the P0420.

 

Thanks so much for the help- followed the procedure for cleaning the IACV valve this morn and so far runs like a charm! U guys are lifesavers- have used Car MD for the last 70k for error codes and usually have been right on ie. air sensors,mass air flow -but the cat converter didn't quite sound right thank god- thanks again until next time Big Al

 

Don't dance just yet, some readiness monitors can take well over 100 miles before they're ready to throw that code again.

I hope it was as simple as cleaning the IACV for your sake tho!