Parts for your 2004 Subaru Impreza-Throttle position sensors

2004 Subaru Impreza throttle-position-sensors (TPS): what they do and how to look after them

Technical sources confirm the 2004 Subaru Impreza is fitted with throttle-position-sensors. The Subaru Factory Service Manual for 2004MY Impreza (Engine Control/Diagnostics sections) details TPS operation and diagnostics, including DTCs P0120–P0124. Wiring and diagnostic data in professional databases such as Subaru Tech Info, Mitchell1 and ALLDATA DIY also show TPS signal circuits across 2004 Impreza variants. Cable‑throttle models (most 2.0/2.5 NA and 2004 WRX) use a conventional TPS on the throttle body, while the 2004 STi’s electronic throttle control uses dual TPS elements built into the throttle body alongside a pedal position sensor. So yes—this part is relevant and used on the 2004‑Subaru‑Impreza.

The TPS tells the ECU exactly how far the throttle plate is open. That live angle signal is key for fuelling, ignition timing, idle control, decel fuel cut, and auto trans shift strategy on 4EAT models. Get it right and the car pulls cleanly, idles smoothly and keeps fuel use in check. Get it wrong and there’s hesitation, surging or a stubborn check‑engine light.

On cable‑throttle Imprezas, the TPS is a bolt‑on, adjustable sensor on the throttle shaft. Over time, wear or a dead spot in the track can cause flat‑spots off idle or erratic revs. On STi with drive‑by‑wire, the throttle body houses dual TPS channels for redundancy, if the channels disagree, the ECU drops into limp mode. In both cases, the TPS signal should sweep smoothly from closed to wide‑open, matching the spec in the Subaru manual.

• Common signs it’s time: check‑engine light (P0120–P0124), rough idle, stumble on tip‑in, poor fuel economy, kickdown confusion on autos, or sudden limp mode on DBW cars.
• Quick checks: inspect the connector under the bonnet for corrosion, make sure the throttle body is clean (don’t drown the sensor in cleaner), and verify smooth TPS signal with a scan tool.

Replacement and service tips for a 2004‑Subaru‑Impreza throttle‑position‑sensor: use quality parts, follow the FSM torque and adjustment procedure, and, on cable‑throttle models, set the base position so closed‑throttle voltage is within Subaru spec. For DBW STi, the TPS is integrated, replacement typically means swapping the throttle body assembly and performing an idle/throttle relearn with a scan tool. After any TPS work, clear codes and road‑test over a few kilometres to let trims settle.

Look after the electrical connectors, keep the throttle body clean, and check TPS data as part of routine servicing—easy wins that keep an Impreza happy on Aussie and Kiwi roads.

Does a 2004 Subaru Impreza have a throttle-position-sensor?

Yes. Cable‑throttle models use a stand‑alone TPS on the throttle body, while the 2004 STi’s electronic throttle uses dual TPS elements inside the throttle body. This is documented in the 2004 Subaru service manual and reflected in common OBD‑II codes P0120–P0124.

What are the symptoms of a failing TPS on a 2004 Impreza?

Expect hesitation off idle, erratic idle speed, poor fuel economy, and a check‑engine light. A scan tool will often show a jumpy or inconsistent throttle angle at steady pedal. On DBW cars, disagreement between TPS channels can trigger limp mode.

Can it be driven with a bad TPS, and what does replacement involve?

It might drive, but not happily—and it can be unsafe if it surges or drops into limp mode. Cable‑throttle cars typically need the sensor replaced and adjusted to spec. STi DBW units are usually replaced as a throttle body assembly, followed by an idle/throttle relearn and code clear.