The throttle position sensor on your 1998 Civic is responsible for sensing how open the butterfly valve is, inside the throttle body. The TPS receives a 5-volt signal from the vehicle computer and it returns a voltage output to the computer that changes along with the opening and closing of the butterfly valve -- 0.9 volts at idle to 5 volts at full throttle. The computer then uses this voltage to adjust the ignition system accordingly. Replacing a failed TPS on your 1998 Civic is easy, once you know where to find it.
Open the hood and find the throttle body -- the component that is just behind the engine and that the accelerator cable connects to. Find the electrical component on the opposite side of the throttle body from the accelerator cable; this is the throttle position sensor.
Press and hold the unlocking button on the TPS wiring harness, and unplug the harness from the TPS. Remove the two screws securing the TPS to the throttle body, using a ratchet and socket. Pull the TPS away from the throttle body to remove it.
Align the new TPS with the shaft on the throttle body and guide the TPS into place. Tighten the TPS screws until they are snug, using a ratchet and socket, and plug the wiring harness into the TPS.
