I was cleaning and detailing my 2.8L engine last night and when I removed the distributor cap and plug wires, I noticed an 1/8 dia hole in the plenum. The hole was located by the throttle body at the neck. Is this suspossed to be there? Please inform. Also, what is the best way to clean the inside of the plenum. I cleaned the throttle body and there was a lot of carbon deposts and I'm sure that it is all though the system. One time I was watching Shadetree Mechanic and they had a system that cleaned all of the carbon out. They hooked a device up to the fuel system and the car ran off of a canister of cleaner and when it was empty, the system was cleaned. If anyone knows what this is, please let me know. the oi

Bengal, I have the same on my plenum. I think it is due to a bolt that fits in that area. My local GM guy said it is not a problem.

Check with a local oil cange station(jiffy lube). They have that fuel system cleaner that you were referring to.
I just cleaned mine with carb cleaner as best I could. I cleaned most of it with the engine off and then started it and sprayed down in there while giving it throttle.
Black stuff came out the exhaust.
It does seem the run alittle better.

Ed Parks form the fiero factory sells a kit that will thouroghly clean out all the carbon deosits in the upper and lower intake, valves and the top of the pistons for about $40. People say their cars have never ran so well afterwards.

http://www.welcome.to/thefierofactory