* Throttle Position Sensor (TPS): The TPS tells the computer the throttle's position. A faulty TPS can send incorrect signals, leading to a lean or rich mixture at part throttle. This is a very common cause of rough running in this scenario.
* Idle Air Control (IAC) valve: The IAC regulates air flow at idle. If it's dirty, sticking, or failing, it might not be able to smoothly transition from idle to slightly higher RPMs, causing a rough running condition.
* Fuel Pressure Regulator: A faulty fuel pressure regulator could cause inconsistent fuel pressure, especially under light load. Too low and you get a lean mixture; too high and you might get a rich mixture, both resulting in rough running.
* Vacuum Leaks: Leaks in the intake manifold, vacuum lines, or even a cracked PCV valve can disrupt the air/fuel mixture, particularly noticeable at low loads where the vacuum is significant.
* Dirty Throttle Body: A dirty throttle body can restrict airflow, affecting the air/fuel mixture. Cleaning it is a relatively simple maintenance task.
* Mass Airflow Sensor (MAF) - Less Likely (but possible): While less likely on a TBI system (which uses a MAP sensor instead of a MAF), a failing MAF sensor *could* still contribute to problems, though it's more common to see issues at higher RPMs.
* MAP (Manifold Absolute Pressure) Sensor: The TBI system uses a MAP sensor to determine engine load. A faulty sensor will give the computer incorrect information leading to poor fueling.
Troubleshooting Steps:
1. Check for vacuum leaks: Visually inspect all vacuum lines and the intake manifold for cracks or loose connections. Use a vacuum gauge to check for leaks if you have one.
2. Clean the throttle body: Remove the throttle body and clean it thoroughly with throttle body cleaner. Pay close attention to the IAC valve.
3. Check fuel pressure: Use a fuel pressure gauge to measure fuel pressure at idle and under light load. Compare to the specifications in your repair manual.
4. Test the TPS: Use a multimeter to check the voltage output of the TPS at different throttle positions. Compare to the specifications in your repair manual.
5. Inspect and clean the IAC valve: Make sure it moves freely and isn't sticking. Cleaning it might be sufficient; replacement might be necessary if it's severely damaged.
6. Check the MAP sensor: You'll likely need a scan tool or a multimeter to check the MAP sensor signal. Compare the values to the specifications in the repair manual.
Important Note: Without proper tools and knowledge, diagnosing these issues can be challenging. If you're not comfortable working on your vehicle's fuel system, it's best to take it to a qualified mechanic. Incorrectly diagnosing or working on the fuel system can lead to engine damage.
