I been noticing rough idle when start up. Few weeks ago I got a 02 sensor code I cleared and never came back . Now today I started the car and it stalled right away. Restarted it and cel was blinking with rough idle. Restarted again and cel went on with out blinking. Have a po300-po304 codes that I just erased. What could be causing this? Service records show tune up at 100k now have 170k miles

 

Install new Toyota spark plugs (Lexus or Toyota dealer only due to Chinese counterfeits on Ebay and Amazon). Also clean your MAF and install a new air filter.

 

It happens more when the car sits for a couple days I don't use your everyday

 

The GS 300 is susceptible to carbon buildup on the valves, due to direct injection, these codes would make me look there. The 350 has an extra set of injectors to clean the valves (other reasons too). Maybe get one of those inexpensive borescopes and check when you pull the intake. THere are chemicals that supposedly help this issue, I have never tried them though. Start by seafoaming the intake, that would be a first step.