grounded1 yes big improvement idling smoother,more acceleration,yes there is a notable differance.actually this stuff they use is not a fuel additive it is in a spray can and they sray it in the plastic pipe that goes into the exhaust manifold apparently
all the instructions are on the back of can in australia the can of stuff they use is only au$16.00 and they will do it for you for a pretty reasonable price they test drive car after jobs done and give you a report i let them do it because they do it to ej22 engines all the time when needed they do suggest use it every
service or six months they also said if problem becomes persistant
the car might need a in car engine clean out.give it a try $16.00
bucks here is nothing only $8.00 bucks in the USA hope it works
ps/ they also suggest shell optimax fuel apparently it helps clean the valves and other gunk.good luck col.