* Idle Air Control (IAC) Valve: This is the most likely culprit. The IAC valve controls the amount of air entering the engine at idle. If it's dirty, stuck, or malfunctioning, it won't supply enough air to keep the engine running at idle speed. Cleaning it (carefully) is often the first step. If cleaning doesn't work, replacement is necessary.
* Throttle Position Sensor (TPS): The TPS tells the ECU the throttle's position. A faulty TPS can give incorrect readings, causing the ECU to not supply the correct fuel/air mixture at idle. This needs testing with a multimeter or replacement.
* Fuel Pressure Regulator: While less likely, a faulty fuel pressure regulator could lead to insufficient fuel at idle, causing the engine to stall. This would usually manifest as other symptoms as well, like poor acceleration. Checking fuel pressure is necessary to rule this out.
* Vacuum Leaks: Small vacuum leaks can disrupt the air/fuel mixture, especially at idle. Inspect all vacuum lines for cracks or loose connections. Pay close attention to the lines leading to the IAC valve and the fuel pressure regulator.
* Dirty Fuel Injectors: While less likely to cause this *specific* problem, very dirty injectors could contribute to poor idle. Cleaning or replacing them might help if other things are ruled out.
* ECU Issues (less likely): A problem with the engine control unit itself is less common but possible. This is usually diagnosed by process of elimination, ruling out other, more likely issues first.
Troubleshooting Steps:
1. Check for vacuum leaks: Visually inspect all vacuum lines and connections. You can use a propane torch (carefully!) to check for leaks near the intake manifold (the propane will change the engine's idle if it's drawn into a leak).
2. Clean the IAC valve: Locate the IAC valve and carefully clean it using carburetor cleaner or a similar solvent. Be gentle and don't damage the delicate parts. Reinstall and test.
3. Check the TPS: This usually requires a multimeter to test its voltage output. You'll need a workshop manual or online resources specific to your RX-7 to find the testing procedure and specifications.
4. Check fuel pressure: This requires a fuel pressure gauge and may require a specialized fitting depending on your car.
If cleaning the IAC valve doesn't solve the problem, and you're not comfortable working with fuel systems or electronics, take it to a mechanic specializing in rotary engines. These are more complex engines, and improper diagnostics can cause further damage. A professional will have the tools and experience to diagnose and repair the issue efficiently.
