Have been having same problem. With car sit they took to dealer replaced about 4000$worth of parts then offer to buy when could not fix.Remove air cleaner. The throttle position sensor >is under where air comes in, rubber boot w/clamp wire goes toward fuel pres regulator (4)prong>make sure air line from valve cover (where air cleaner hooks to valve cover) that line goes to fuel pres.reg.> idle control valve (3/4 line in and out) is close to F.P.R.
OVP (over volt.prot.) is behind battary has (RED)top 2 fuses (or-1) push in tipe (gm) 10 amp. Don't feel bad have 5 hrs trying to fix one i am working on.its goten better but no silver star yet.been working on benzs 28years know Worker on 8-9 300 from 50's i love working on them this my 3rd 88-91 300.What nice for me is have 89-300 parts car,300 engine out of car ran good blown head gasket. So i can swap parts 3sets of wires cap rotor>coils>control boxes>conplete fuel systems. Hoping to day to fix.