* Idle Air Control (IAC) Motor: This small motor regulates the amount of air entering the engine at idle. A dirty or faulty IAC motor can prevent the engine from maintaining a consistent idle speed. It might be sticking, dirty, or have failed internally.
* Throttle Position Sensor (TPS): The TPS tells the computer the position of the throttle plate. A faulty TPS can give inaccurate readings, causing the computer to provide incorrect fuel and air mixtures at idle.
* Mass Airflow Sensor (MAF) Sensor: The MAF sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can lead to a lean air/fuel mixture, causing the engine to stall at idle.
* Vacuum Leaks: A leak in the vacuum system can disrupt the airflow to the engine, making it difficult to maintain idle. Check all vacuum hoses for cracks, holes, or loose connections. Pay close attention to the brake booster hose.
* Fuel Pressure Issues: While less likely to cause the engine to die *only* when the gas pedal is released, low fuel pressure can contribute to poor idle. This could be due to a failing fuel pump, clogged fuel filter, or other fuel system problems.
* PCV Valve: A clogged Positive Crankcase Ventilation valve can cause excessive pressure buildup in the crankcase, affecting engine operation and potentially leading to idle problems.
Troubleshooting Steps (in order of easiest to hardest):
1. Check for vacuum leaks: Visually inspect all vacuum hoses. Listen carefully near the intake manifold and vacuum lines with the engine running for any hissing sounds.
2. Clean the IAC motor: This is often a simple fix. Disconnect the IAC motor, carefully clean it with a suitable cleaner (brake cleaner is often used), and reconnect it.
3. Clean the MAF sensor: Use MAF sensor cleaner (NOT brake cleaner) and carefully clean the sensor element. Be gentle!
4. Check the TPS: This often requires a multimeter to check the voltage output at various throttle positions. A faulty reading often points to replacement.
5. Check fuel pressure: This requires a fuel pressure gauge. Low pressure suggests problems with the fuel pump, filter, or regulator.
6. Replace the PCV valve: A relatively inexpensive part that is easy to replace.
If you're not comfortable performing these checks yourself, take your Jeep to a qualified mechanic. They'll have the tools and expertise to diagnose the problem accurately and perform the necessary repairs. Improper diagnosis can lead to unnecessary parts replacements. Remember to specify the symptoms clearly – that the engine starts but dies unless the gas pedal is depressed.
