* Throttle Cable Sticking/Binding: This is the most likely cause. When the engine is running, vacuum and engine movement can put slight tension on the throttle cable, making it harder to push the pedal. When the engine is off, this tension is released, and the pedal feels normal. Look for kinks, fraying, or binding points in the throttle cable. Lubrication might help temporarily, but a replacement is usually the best long-term solution.
* Throttle Body Issues: A sticky or dirty throttle body can cause resistance. Carbon buildup or sticking components within the throttle body can create friction, making the throttle plate harder to move. Cleaning the throttle body with a throttle body cleaner is often the solution here. However, if there's significant damage or wear, replacement may be necessary.
* Vacuum Leaks: While less likely to directly affect pedal feel, significant vacuum leaks can alter engine behavior and might indirectly contribute to a stiffer pedal if they are causing increased tension on the throttle system.
* Throttle Position Sensor (TPS): A faulty TPS is less likely to cause a hard pedal, but a problem with it could be contributing to other symptoms that *indirectly* feel like a stiff pedal due to unusual engine response. This would require diagnostic testing.
* Brake Booster Vacuum Leak (Less Likely): A major leak in the brake booster vacuum line *could* cause unexpected vacuum pressure fluctuations affecting the throttle system, though this is less common.
Troubleshooting Steps:
1. Inspect the Throttle Cable: Visually examine the throttle cable for any obvious damage, kinks, or binding points. Try to gently move the cable by hand (with the engine off) to feel for resistance.
2. Clean the Throttle Body: Use a throttle body cleaner (available at most auto parts stores) to thoroughly clean the throttle body. Make sure to disconnect the battery negative terminal before doing this. Refer to your owner's manual or a repair guide for the correct procedure.
3. Check for Vacuum Leaks: Listen carefully around the engine for any hissing sounds which might indicate a vacuum leak. This is more difficult to diagnose without specific tools or experience.
4. If problems persist: Have a mechanic diagnose the issue. They have tools and expertise to test the TPS and other components, which may require more advanced diagnostic equipment.
Remember safety first! Always disconnect the negative battery terminal before working on any electrical or fuel system components. If you are not comfortable working on your car, take it to a qualified mechanic.
