Idles Great, But Surges When You Give It Gas

It sounds like you have taken some great steps in troubleshooting the issue with your 1994 Toyota T100. The code P0120 indicates a problem with the Throttle Position Sensor (TPS) circuit. Since you have already replaced the TPS and cleaned the throttle body, there may be a few other possibilities to consider:

1. Wiring issue: Check for any loose or damaged wires that are connected to the TPS. Ensure that all connections are secure and free from corrosion. Sometimes, a faulty or damaged wire can cause intermittent connection issues, leading to surging and loss of power.

2. Incorrect installation: Double-check that the TPS was installed correctly. Ensure that it is aligned properly and that all mounting screws or bolts are tightened to the manufacturer's specifications. An incorrectly installed TPS can lead to inaccurate readings and performance issues.

3. Intake manifold leak: A leak in the intake manifold can cause inconsistent intake pressures, leading to surging and poor performance. Inspect the intake manifold gasket and the areas where it connects to the engine for any signs of leaks or damage.

4. Faulty throttle body: Even after cleaning the throttle body, there may be internal issues with it that are causing the surging and lack of power. Consider having it inspected by a professional or replacing it if necessary.

If you have tried these steps and are still experiencing the issue, it would be advisable to consult a qualified mechanic or Toyota dealership. They will have the expertise and specialized diagnostic tools to pinpoint the exact cause of the problem and provide a solution.

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A bad throttle position sensor is the last thing that you will ever wish to have on your ride. The purpose of a throttle position sensor is to keep your car running like it's supposed to by controlling the throttle.

With the passage of time, the sensor will start to get worn and may eventually have to be replaced. The important question is how to identify any bad throttle position sensor symptoms so that you end up replacing the right sensor?

Honestly speaking, it is not easy to detect throttle position sensor issues. However, there are specific throttle position sensor signs to look for to help ensure you find the culprit.

Table of Contents

What Does a Throttle Position Sensor Do?

The primary purpose a throttle position sensor (TPS) is to give information to the car's computer about the throttle. It senses the air, heat, and light, and sends the information to the ECM which adjusts the throttle and fuel supply accordingly.

All vehicles have something called a "throttle" which controls how much fuel is allowed to flow into the engine. The throttle position sensor is what monitors the throttle position from the shaft.

Basically, this sensor is connected to a computer inside the vehicle which shares information sent by the driver. This information contains the actions of the driver such as accelerating, power steering and so forth.

So anytime you step on the gas pedal to accelerate your vehicle, the computer sends this information to the sensor so that the throttle knows how much fuel to let flow into the engine.

In the old days, there used to be a cable that was connected from the throttle to the accelerator. But now in the technological age, the car's computer controls when the throttle opens and closes by the feedback it gets about the acceleration of the vehicle.

Top 6 Bad Throttle Position Sensor Symptoms

A faulty throttle position sensor sends incorrect information to the ECM resulting in various issues in the engine, its performance, and fuel economy.

Below are common symptoms of a faulty TPS. In most of the cases, all of these symptoms will show together making it easier to detect the faulty component.

1) Car Jerks

Jerking or bucking of the vehicle is the most common symptom of a bad TPS. These jerks can be experienced during hard acceleration or when under moderate load.

What makes diagnosing it tricky is that the bucks and jerks may be completely random and not even occur for some stretches of time. The reason this happens is that the ECM doesn't get correct information from the TPS as to how much to throttle the car.

2) Idle Surging

Idle surging can be caused due to other issues in the car, but if it happens in conjunction with other throttle position sensor symptoms, the culprit is often the TPS.

At idle, the ECM will not get the correct information and the throttle will variate randomly causing idle surges.

3) Check Engine Light

The check engine light will randomly turn on and off even if the car is running smoothly without any jerks and stalling. This is often the first ever symptom of a bad TPS.

Using a code reader, you should be able to confirm whether a faulty TPS is the culprit or a different component. Diagnostic trouble codes P0120, P0121, P0122, P0123, and P0124 are what will commonly appear.

4) Engine Stalling

The engine can stall for no reason and without any warning. This happens when the TPS gives incorrect information to the ECM. The engine can stall at high speed, at low speed, or even at idle.

5) Acceleration Issues

A faulty throttle position sensor will not let your car accelerate normally. Though this doesn't happen all the time. You may experience slow acceleration, acceleration surge at both high and low speeds, hesitation or delay in acceleration, and other related symptoms.

6) Problems Switching Gears

The issues with acceleration can lead to gear transmission problems as the ECM doesn't get the correct information about the acceleration. This leads to incorrect shift points which can cause both early or delayed shifts.

Can You Fix a Bad Throttle Position Sensor?

As soon as you see a mix of these throttle position sensor symptoms, you should test the TPS and if it isn't functioning properly, it needs to be replaced. Unfortunately, a TPS cannot be repaired as it is a tiny sensor but the good news is that a new sensor "usually" isn't too expensive so you can get back on the road soon enough.

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