1. Vacuum Leaks:
* Where to Look: Inspect all vacuum hoses, especially those connected to the intake manifold, brake booster, and emissions systems.
* How to Test: Listen for hissing sounds around the engine when it's running. Spray a small amount of carburetor cleaner or brake cleaner around suspected leak points. A sudden change in engine RPM indicates a vacuum leak.
2. Fuel Delivery Problems:
* Fuel Pressure: Check the fuel pressure at the fuel rail. Ensure it's within the manufacturer's specifications.
* Fuel Filter: A clogged fuel filter can restrict fuel flow. Replace it if necessary.
* Fuel Injectors: Inspect fuel injectors for leaks or clogging. You can have them cleaned or replaced.
3. Ignition System:
* Spark Plugs and Wires: Check the condition of spark plugs and wires. Replace if necessary.
* Ignition Coil: Test the ignition coil for proper output.
* Distributor (if applicable): Inspect the distributor cap, rotor, and timing belt for wear or damage.
4. Throttle Position Sensor (TPS):
* Function: The TPS tells the ECU the throttle position. A faulty TPS can cause idle issues.
* Testing: Use a multimeter to check if the TPS is providing the correct resistance values at different throttle positions.
5. Engine Control System (ECU):
* Compatibility: Double-check that the ECU is compatible with the 1988 engine. Even if it's from the same model year, there may be minor variations.
* Programming: If you replaced the ECU, ensure it has the correct programming for the specific engine and vehicle.
6. Engine Mechanical Issues:
* Valve Timing: Incorrect valve timing can severely affect idle. Check and adjust timing if necessary.
* Compression: Low compression in one or more cylinders can lead to poor idle. Perform a compression test.
Troubleshooting Tips:
* Start with the basics: Check for any loose or disconnected wires, hoses, and connectors.
* Use a code reader: Scan the car's OBD-II system for any stored trouble codes.
* Work systematically: Eliminate one possible cause at a time to narrow down the problem.
* Consult a repair manual: Use a repair manual specific to your 1989 RX-7 for detailed troubleshooting information and specifications.
Important Note: If you are not comfortable working on your vehicle, it's best to take it to a qualified mechanic for diagnosis and repair.
