Our 2004 RX330 FWD with a 3.3L engine was purchased used from the original CA owner in 2015 with 127,000 miles. Dash warning lights (check engine, VSC, ABS) started coming on intermittently, bought a code reader which shows P0430 (Catalyst system efficiency behold threshold bank 2). I can erase the code and it may stay off for a day, a week, two weeks or one time, drove from MN to CA 2200 miles over four days and it never came on until one day after arriving at our CA home. It gets 24 mpg at 78 mph and 19 mph in town, starts and runs perfectly. Because it is in such wonderful condition, we intend on keeping it.

It now has 250,059 miles and has been maintained to the highest degree with no winter salt exposure, original running gear, exhaust and suspension. One master mechanic, pulled the P0430 code and did a pressure check (ok) and replaced one sensor and suggested we use a fuel cleaner additive, which we did and a week later, same lights/code popped up and keep appearing intermittently ever since At 132,248 miles, replaced spark plugs (Iridium) and intake plenum gasket. At 150,554 replaced valve cover gaskets. At 179,513 replaced timing belt, water pump, coolant. At 204,094 replaced spark plugs (Iridium), upper intake gasket set, both throttle body gaskets, cleaned fuel injectors. At 208,300 replaced bank 2 catalyst with a Walker brand, same issue. Replaced all four cat sensors with Denso units...no help. At 233308 miles, replaced intake manifold gasket, thermostat, cross pipe water hose, coolant. At 249215 replaced air flow meter, no help. Denso products were used wherever possible. Intake air filters replaced as required. We use Top Tier fuel and drive normally with occasional light towing.

I'm a retired outboard motor mechanic and am astute about keeping our vehicles in top condition, but this cat warning system has not only me stumped, but also five more certified repair shops as well. My only thought is that we have a bad electrical ground somewhere. The car won't pass CA smog tests, so can't get it licensed in CA. MN does not have smog tests, so it remains registered there (our legal residence). Any ideas? Thanks

 

When you say Iridium, which plugs exactly? There are dozens of choices in plugs that have all manner of description. Where did you buy the Denso parts? If Amazon or Ebay you bought fakes. Have you ever looked a the VVTi oil control valves?

 

Denso plugs and parts, all in genuine Denso packaging. Why do you question my selections? I am a former mechanic and very astute about parts. I have purchased many parts from trusted (highly rated) vendors through the years without a single quality issue. If I may pose this question; if you or I had work done at a dealership, what guarantee is there that they use genuine parts? There are crooked dealers, you know. (I was a car salesman at several car dealerships and I can attest that I saw them cheat their customers over and over; one (a Ford dealer) was taken to court by the county for falsifying squad car equipment. He lost. He paid. Dearly.

 

Ditto.....Have you looked at the vvti valves? You possibly might have a problem removing them as they might be gummed/stuck.