Hello from Downunder Australia

1) what exactly is error code?
2) not sure what you mean with "manifold vacuum inlet". there is vacuum pump for brakes, but I don't think it is connected to intake. why?

The error code is P0420.
Generally I put the additives in the tank.

But one of my friends inject the this fluid via manifold inlet in Forester and it half the engine what it says on the bottle.

when I take off the vacuum hose from engine even without adding anything it should halt the engine. So was thinking if I can add it via hose it will go straight to the sensors.
Thanks

I didn't understand that "it half the engine what it says"...

anyway, I did twice add aceton to fuel tank and it healed that P0420.

straight to the sensors - lambda sensors are in exhaust. so... adding them to intake is not "straight to the sensors".
to my understanding - aceton makes combustion to be with higher temperature and that higher temperature burns dirt on lambda sensors and catalysts.

apologies for spell mistake - " "it halt the engine what it says on the bottle

ACETON - what is the ratio you used or how much you added in tank and how much was the fuel in the tank?

Thanks

wow... basically your buddy gave hydroshock to engine... yep... not a good idea. I wonder why he didn't do as all "normal" people do - pour it into tank?

Aceton ratio I used was 1:10 by volume(1qt aceton to 10qt of gas). first time I used some kind of diluted acton (paint thinner, I think - it had like 50% aceton concentration) - second time pure. recommended method is - add it when your gas is almost empty. drive it ASAP - the higher load(revs) the better. start-stop in city traffic is bad idea. when tank is empty - fill it with fresh gas and you are good to go.