Thanks to this posting I was able to save and solve this simple problem after the oil change and air filter removal. I want to emphasize the point that the battery must be disconnected to reset the check engine light.
After this repair I went underneath to get fimilar with the car, and I saw a hose tube coming from the center what appears to be the transmission. This tube connection was not attached to a hose and I could not find one either. I would like to find access to the exploded views of the RS 300 models.
Does anyone know where I can find access? I am certain the dealers have access and may ask about the tube issue at my locate dealer.
I do not think it is a drain tube and the check engine light is not on now. The tube fitting appeared to have a tube because it looked clean and had marks that looked like a hose may have ben removed during the oil change.
I must add the area around this hose connect was very clean anyway, so I may be worring about a drain/vent type connection.
Again I thank you all that post and help others with their fine Lexus cars and SUVs, solve issues that many of us can follow.