Hi, I have a 1994 GMC Jimmy
4.3 Vortec W code. The Jimmy idles rough, it shakes, and idles up and down. It revs to high rpms without trouble and seems to smooth out when brought just off idle. When it idles up and down the oil gage goes between 40 and 5. When I drive it and floor the gas pedal it seems to have just about the same power as before the idling problem. when I let off of the gas to slow down it idles low enough that the brake
pedal gets hard and the engine
sometimes dies. The check engine light only comes on when the thermostat opens. I have checked the code (obd1) and get a map sensor low voltage code, a idle air control low voltage code, and a tps low voltage code.
I have replaced the ground strap, idle air control, map sensor, tps sensor, ecm, distributor, egr, coolant
temp sensor, knock sensor, alternator
, plugs, wires, cap, rotor button, ignition control module, spider injectors, nut kit, upper intake gasket, and brake booster check valve. I have unplugged the o2 sensor
which didn't make a difference. I believe that there has to be a short in the wiring but am unsure what wires or wire to check that would effect all of these sensors. The only problem that I have had that is electrical so far is with the tail lights I replaced the blown taillight fuse and it seems to have fixed it. The taillights and dash lights went out when the fuse blew, I haven't been able to drive it long enough to see if it is still a problem. It blew when I went over a rough bridge......