* Fuel Pump: A weak fuel pump may not provide sufficient pressure to the injectors at idle, requiring you to pump the gas to build pressure momentarily. Once the initial pressure is built, the engine can start, but the weakening pump can't maintain it for idling.
* Fuel Injectors: Clogged or malfunctioning fuel injectors can prevent the proper amount of fuel from being delivered at idle speeds. Pumping the gas might momentarily overcome this, but the issue persists once the engine tries to maintain a consistent, lower RPM.
* Air Flow Meter (AFM) or Mass Air Flow Sensor (MAF): If your RX-7 has an AFM (more likely in a '90 model), a dirty or faulty AFM won't accurately measure the incoming air, leading to an incorrect fuel mixture. A bad MAF sensor (if it's equipped with one instead) will cause similar problems. At idle, the inaccurate reading is magnified, preventing proper idling.
* Throttle Position Sensor (TPS): The TPS tells the ECU the throttle position. A faulty TPS sends inaccurate information, causing the ECU to provide incorrect fuel delivery. This often leads to rough idle or no idle at all.
* Idle Air Control Valve (IACV): This valve controls the amount of air bypassing the throttle at idle. A dirty or faulty IACV can prevent the engine from maintaining a consistent idle speed. It's a very common culprit in this situation.
* Vacuum Leaks: Leaks in the vacuum system can dramatically affect the air/fuel mixture, causing erratic idling and starting difficulties. Inspect all vacuum lines and connections for cracks or disconnections.
* Fuel Pressure Regulator: A failing fuel pressure regulator can cause inconsistent fuel pressure, leading to similar problems.
* ECU Issues: While less common, a malfunctioning Engine Control Unit can also contribute to these symptoms. This is usually diagnosed after checking all other components.
Troubleshooting Steps:
1. Check for Vacuum Leaks: Visually inspect all vacuum lines and connections. Use a propane torch (carefully!) to check for leaks – the engine RPM will change if the propane is sucked into a leak.
2. Check the Fuel Pressure: Use a fuel pressure gauge to measure fuel pressure at idle and at higher RPMs. Compare your readings to the factory specification.
3. Clean the IACV: This is often a quick and easy fix, and relatively inexpensive to have done if you're not comfortable with the repair.
4. Inspect the AFM or MAF: Clean the AFM (or MAF) sensor element with MAF sensor cleaner.
5. Check the TPS: You might need a multimeter to check the voltage output of the TPS across its range of motion.
6. Inspect and/or replace fuel filter: A clogged filter can restrict fuel flow.
Because this is a rotary engine, some of these issues might manifest differently compared to a piston engine. Finding a mechanic with experience in rotary engines (specifically 13B engines) will significantly improve your chances of quick and accurate diagnosis. A proper diagnostic scan tool that can read codes from the ECU is also very helpful.
