1. Verify Fuel Pump Installation & Operation:
* Correct Installation: Double-check that the fuel pump is correctly seated, all connections are secure (electrical and fuel lines), and there are no leaks. A wrongly installed pump can cause a variety of problems, including poor fuel delivery.
* Fuel Pressure: You need a fuel pressure gauge to measure the fuel pressure at the fuel rail. Your car's specifications should indicate the correct pressure. Low pressure is a major cause of rough idling. If the pressure is low, it could indicate a problem with the pump itself (despite the new replacement), a clogged fuel filter, or a faulty pressure regulator.
* Fuel Pump Relay: The fuel pump relay controls power to the pump. A bad relay can cause intermittent or complete pump failure. You can try swapping the relay with a known good one from another circuit (check your owner's manual or a wiring diagram to find a compatible relay).
2. Beyond the Fuel Pump:
* Fuel Filter: A clogged fuel filter restricts fuel flow, leading to rough idling. Replace the fuel filter – it's a cheap and easy fix that often gets overlooked.
* Air Filter: A dirty air filter restricts air intake, causing a lean fuel mixture and rough running. Replace it with a new one.
* Throttle Body: Clean the throttle body. Buildup of carbon deposits can interfere with the idle air control system. Use throttle body cleaner and follow instructions carefully.
* Idle Air Control (IAC) Valve: The IAC valve regulates air flow at idle. A malfunctioning IAC valve often results in rough idling, stalling, or high idle. This might need cleaning or replacement.
* Mass Airflow Sensor (MAF) Sensor: The MAF sensor measures the amount of air entering the engine. A faulty sensor can lead to incorrect fuel mixture and a rough idle. It's best to have this tested or replaced if suspected.
* Spark Plugs and Wires: Worn spark plugs or faulty ignition wires can cause misfires leading to rough idling. Check the condition of your plugs and wires; replace if necessary.
* Distributor (if applicable): If your engine has a distributor, check the cap and rotor for wear or damage. A faulty distributor can cause misfires.
* Vacuum Leaks: Check all vacuum hoses for cracks or leaks. A vacuum leak can disrupt the proper air/fuel mixture.
* Computer Issues: Although less likely, a problem with the engine control module (ECM) could be responsible. This is generally more difficult to diagnose and requires specialized equipment.
Troubleshooting Steps:
1. Start with the easiest and cheapest: Check the fuel filter and air filter first.
2. Check fuel pressure: This is crucial to eliminate the fuel pump as a suspect.
3. Visually inspect: Look for any obvious problems like loose connections, vacuum leaks, or worn parts.
4. Use a diagnostic tool: A scan tool can help diagnose trouble codes from the engine's computer, pointing to potential problems.
If you've checked all of these and the problem persists, it's advisable to take your car to a mechanic for further diagnosis. Trying to fix complex engine problems without the proper tools and knowledge can be frustrating and potentially lead to further damage. Remember safety first – always disconnect the negative battery terminal before working on any electrical components.
