water in the intake
I've seen an old timer mechanic do that trick to decarbonize big block chevrolets. He sprayed with a hose on about 1/3 and held his thumb over the end of the hose. He sprayed intermittently and didn't use very much water, but I saw steam come out the exhaust pipe. The car idled and ran much better after this. He did remind me not to use too much water though.
1986 300E 88k
1999 Crew Cab Dualie Chevrolet 7.4L