Vacuum Leaks: This is HIGHLY probable. Vacuum leaks can cause erratic idle speeds, including racing. Check all vacuum hoses and connections for cracks, splits, or loose fittings. Pay close attention to:
* Brake booster hose: A common point of failure.
* Hoses to the intake manifold: Look for any that are brittle, cracked, or disconnected.
* Vacuum advance on the distributor: If equipped, check its connection.
Idle Air Control (IAC) Valve: This valve regulates air flow at idle. A dirty, sticking, or faulty IAC valve can cause a high idle. Cleaning it (with appropriate cleaner) is a good first step, but replacement might be necessary.
Mass Airflow (MAF) Sensor: While less likely if the TPS is new, a dirty or faulty MAF sensor can send incorrect air/fuel mixture signals, leading to an erratic idle. Cleaning it (carefully, following instructions) is worth trying.
Throttle Body: Even with a new TPS, a dirty or sticking throttle body can prevent the throttle plate from closing completely. Thorough cleaning is essential.
PCV Valve (Positive Crankcase Ventilation): A clogged PCV valve can create excessive crankcase pressure, affecting the engine's idle.
Vacuum leaks within the intake manifold: These can be harder to find and often require a smoke test to pinpoint the location.
Wiring and Connections: Double-check all wiring harnesses and connectors related to the TPS, IAC, and MAF. A loose connection or damaged wire can cause erratic signals.
Computer (PCM/ECM): In rare cases, a faulty PCM/ECM can cause these problems. This is less likely than the other issues, but possible. Diagnosing this requires a professional scan tool.
Troubleshooting Steps:
1. Check vacuum lines: This is the easiest and most likely culprit.
2. Clean the IAC valve: This is a relatively easy fix and often solves the problem.
3. Clean the throttle body: This is also straightforward and helps ensure smooth operation.
4. Check/clean the MAF sensor: Be gentle; static electricity can damage it.
5. Inspect PCV valve: Replace if necessary.
6. Visually inspect wiring: Look for any obvious damage.
When to Seek Professional Help:
If you've checked all the above and the problem persists, it's time to consult a mechanic. They have specialized tools (like a vacuum gauge and a scan tool) to diagnose more complex issues. A smoke test can be particularly helpful in finding hidden vacuum leaks.
Remember safety first: Disconnect the negative battery terminal before working on any electrical components.
