AkkiDonz

@ColinBarber
Now i am getting bunch of codes. P0138,P0158 and P0420. 
Before if i reset the codes, it wont show up that quick. Now as soon as i resets it start appearing again. 

Thanks Colin,

I have checked for exhaust leak and they found no leak but some time with open window I can smell nasty but very rare.

will check with O2 sensor.

Hello mates,
First of all i agree there are so many post regarding P0420 and i have tried most of the suggested tricks. I am at the end stage to change my Cat. Before doing that decided to check here for the last opinion. So i only get P0420 code on low boost (city driving). If i reset the code and drive motorways no code. 
I have changed spark plugs, welded the pipe(funny they found leak on bank 2 after o2 sensor), Cataclean, o2 sensor has been replaced by old owner few months back.

Any other suggestion ?

Thanks 

CVT gearbox are nice in terms of quick acceleration, It is made to reduce gear shifting time. I strongly doubt any of the petrol GS MK3 comes with CVT. As you are in a hunt of Lexus made sure you get a car with is compatible with E10 fuel. As UK has made E10 a standard and E5 is only available on Premium grade. I recently Purchased a GS300 and saw 5 to 6 cars and found TPMS is a common error in all the cars.