It is very common for the throttle plate on a old throttle body to freeze up. Get some light lubricating oil on the plate shaft (inside and out) and work it by hand. Once the throttle arm turns freely then replace the cable. Good idea to oil the cable as well. Replacing the cable is not hard but its an involved process as the center console, shift console and the radio console must be removed to access the cable.
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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "