High-Probability Issues:
* Vacuum Leaks: This is the *most common* cause of idle problems in rotary engines. Small leaks in vacuum hoses, the intake manifold, or even around the throttle body can significantly disrupt the idle mixture. Inspect *all* vacuum lines meticulously for cracks, splits, or loose connections. Pay special attention to the lines connected to the Idle Air Control (IAC) valve and the FCD (Fuel Cut Device) if equipped.
* Idle Air Control (IAC) Valve: The IAC valve regulates airflow at idle. A dirty, sticking, or faulty IAC valve will prevent the engine from maintaining a stable idle. Cleaning it (with carb cleaner) is often a simple fix, but it may need replacement if cleaning doesn't help.
* Fuel System Issues:
* Fuel Pressure: Low fuel pressure can cause a rough idle and stalling. Have the fuel pressure checked.
* Fuel Injectors: Clogged or leaking injectors will deliver an inconsistent fuel mixture, leading to poor idle. Injector cleaning or replacement might be necessary.
* Fuel Filter: A clogged fuel filter restricts fuel flow, similar to low pressure. Replace it as a preventative measure.
Medium-Probability Issues:
* Distributor/Ignition System: Worn distributor cap, rotor, or ignition wires can cause misfires, leading to a rough idle. Inspect and replace as needed. The ignition coil should also be checked.
* Compression: While less likely to cause *only* an idle issue, low compression in one or more rotors will impact performance across the RPM range, including idle. A compression test is recommended if other issues are ruled out.
* Throttle Position Sensor (TPS): A faulty TPS can provide incorrect information to the ECU, affecting fuel delivery and idle. Testing the TPS is usually required to diagnose this problem.
Low-Probability Issues (but still possible):
* EGR Valve (Exhaust Gas Recirculation): While less critical on a non-turbo, a malfunctioning EGR valve can impact idle.
* ECU Problems: Though rare, a faulty ECU could be the source of the problem. This is usually diagnosed last after other components have been checked.
Troubleshooting Steps:
1. Visual Inspection: Start by carefully inspecting all vacuum lines, the IAC valve, and the fuel system components for visible damage.
2. Vacuum Leak Test: Use a propane torch (carefully!) or a commercial vacuum leak detector to check for leaks in the vacuum system. A change in idle speed when the propane is near a leak indicates its location.
3. Clean the IAC Valve: This is a simple and often effective solution.
4. Check Fuel Pressure: Use a fuel pressure gauge to verify fuel pressure is within specification.
5. Check Ignition System: Inspect distributor cap, rotor, wires, and coil for wear or damage.
6. Compression Test: If other issues are ruled out, a compression test will reveal the health of your rotors.
Important Note: Rotary engines have specific quirks. Working on them requires some specialized knowledge. If you're not comfortable performing these checks yourself, it's best to take your RX-7 to a mechanic experienced with rotary engines. Attempting repairs without proper knowledge could potentially cause further damage.
