* Ignition Module (or Pick-up Coil): The ignition module (often integrated into the distributor on some models) or the pickup coil (inside the distributor) can be failing intermittently. These components control the spark timing and strength. A failing module can cause misfires, backfires, and rough idling. This is a prime suspect.
* Distributor Shaft Play: Excessive wear in the distributor shaft can cause the rotor to be slightly misaligned, leading to improper spark delivery. This is less likely given the recent distributor cap and rotor replacement, but worth checking for excessive play.
* Worn or Damaged Camshaft Position Sensor (CMP Sensor): The CMP sensor tells the engine's computer the crankshaft position. A faulty sensor will result in poor timing and erratic fuel delivery, causing the symptoms you describe.
* Crankshaft Position Sensor (CKP Sensor): Similar to the CMP, the CKP sensor tells the engine's computer the crankshaft's position. If this is faulty it can lead to timing issues.
* MAP Sensor (Manifold Absolute Pressure Sensor): This sensor measures the air pressure in the intake manifold. A bad MAP sensor provides incorrect data to the fuel injection system, leading to poor fuel delivery and rough running.
* Throttle Position Sensor (TPS): This sensor tells the computer the throttle position. A faulty TPS can cause erratic idle and poor throttle response.
* Vacuum Leaks: Small vacuum leaks can disrupt the fuel/air mixture, leading to a rough idle and backfiring. Inspect all vacuum hoses carefully for cracks or loose connections.
* Incorrect Spark Plug Gap: Even with new wires, if the spark plug gap is incorrect, it can lead to misfires and rough running.
* Faulty Injectors (despite cleaning): Although you cleaned the fuel injectors, one might still be partially clogged or have internal issues.
* Exhaust Leaks: An exhaust leak before the catalytic converter can cause backfires.
Troubleshooting Steps:
1. Check for vacuum leaks: Use a propane torch (carefully!) or vacuum gauge to check for leaks in the vacuum system.
2. Inspect the ignition module/pickup coil: While visually inspecting for damage, consider testing its output with a multimeter or using a known good replacement for testing purposes.
3. Test the CMP and CKP sensors: These sensors can be tested with a multimeter or scanner.
4. Test the MAP and TPS sensors: These sensors can also be tested with a multimeter.
5. Verify spark plug gap: Check the gap against the specifications in your owner's manual.
6. Check for exhaust leaks: Listen carefully for escaping exhaust gases near the exhaust manifold and catalytic converter.
7. Use a code reader (OBD-I scanner): A code reader for your 1991 Camaro will likely retrieve diagnostic trouble codes (DTCs) that can pinpoint the problem area.
It's highly recommended to use a code reader or consult a mechanic experienced with OBD-I systems (your car doesn't have OBD-II). Diagnosing this issue systematically will save time and potentially prevent unnecessary part replacements.
