Hey last week I cleaned out all the carbon from my throttle body and intake manifold from
my 1990 Civic Si. I bet it was never done in 20 years, since there was so much carbon buildup inside the TB and around the throttle plate.
I used a product made by Revive, air intake system cleaner, (found at partsource.)



Works really well to dissolve the carbon, and also used a small toothbrush to loosen up the carbon. I took off the throttle body to clean, but it's not really necessary . You can just spary inside to clean.
After I cleaned out the TB, I then sprayed into the intake manifold chamber, let it sit for a couple minutes and then ran the car for about 5 minutes giving it some gas as well. You notice some black smoke coming out of the tail pipe.
The results were worth it. Better/smoother throttle response, and smoother idle too. Very noticeable results. It's recommended to clean out the throttle body every 20,000 kms or whenever a tuneup is done.