Testing the throttle position sensor on your 1990-1994 Nissan 3.0L Pathfinder (3.0L D21 Pickup) is not hard and can be done with a multimeter. As you're already aware, the TPS is two components in one assembly. One part of the assembly is an idle switch and the other is the throttle position sensor (this is the reason why the TPS assembly has two connectors). In this tutorial, I'll show you how to test the throttle position sensor part of the TPS assembly with 3 simple. With these 3 tests, you'll be able to accurately diagnose the throttle position sensor as bad (or not). In a nutshell, the fuel injection computer on your 3.0L Pathfinder (3.0L D21) needs the throttle position sensor to let it know how much the throttle plate opens or closes as you step on (or off) the accelerator pedal (since the accelerator pedal is connected to the throttle plate via a cable). With the throttle position info the fuel injection computer can now: inject more/less fuel, advance/retard ignition timing, etc. Being that the TPS is a critical input sensor of the engine management system, when it fails your 3.0L Nissan is gonna' resent it. You'll see one or more of the following symptoms: A TPS diagnostic trouble code (DTC) stored in the PCM's memory: