Subaru does an excellent top end cleaner which is designed for just this purpose and is cat convertor safe. I used to work in a large multi car dealership where all the different brands of cars would actually recommend this cleaner (via subaru) for carbon build up in the manifolds/valve backs/throttle body etc. I recall an car once that had a constant idle stutter that couldnt be fixed, the only thing left was to remove the heads and de-carbon and inspect them. Firstly the cleaner was applied through the injector holes over a few hours which fixed the problem. Be aware the cleaner is ment to be burnt by the engine and as it disolves the carbon and should not really be left untill it has dried up but rather burnt by the engine. The car will be very hard to start and once it does will cause huge clouds of smaoke. The cleaner here in Australia is called 'Subaru upper engine cleaner' and comes in a small aerosol can not sure if it is available or called the same in the states. Good luck Nick #10927 To address comments privately to the moderating team, please address: moderators@xxxxxxxxxxx For more info on the list, tech articles, cars for sale see www.dmcnews.com To search the archives or view files, log in at http://groups.yahoo.com/group/dmcnews Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/dmcnews/ <*> To unsubscribe from this group, send an email to: dmcnews-unsubscribe@xxxxxxxxxxxxxxx <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/