Standing in front of the engine facing yor TBI. Remove air cleaner assembly and filter and anything else atop TBI. On the lower right area of the TBI you'll see a round slightly raised dimple area. About the size of a pencil. That's a plug covering your idle adjustment screw. It's not completely flat, kinda protrudes outward a bit. You'll either have to drill it out or CAREFULLY tap it with a hammer and punch. Go easy and tap carefully because that TBI body is not super strong. Crank-break that and its new TBI time quite possibly!
Once you get the plug out, use an Allen wrench to adjust it. Real easy to adjust once you get the plug removed.
I'll try and get you a picture of mine if my digital camera battery isn't dead.