Several things can cause this:
Possible Causes:
* Vacuum Leaks: This is a very common cause. Leaks in vacuum lines, intake manifold gaskets, or even cracked intake manifold runners allow unmetered air to enter the engine, throwing off the air/fuel ratio. Inspect all vacuum lines carefully for cracks, holes, or loose connections. Pay particular attention to the lines leading to the brake booster, PCV valve, and the intake manifold.
* Mass Airflow Sensor (MAF) Sensor: A dirty or faulty MAF sensor can provide inaccurate readings to the engine control unit (ECU), leading to a lean condition. Clean the MAF sensor with MAF sensor cleaner (following the instructions carefully) or replace it if cleaning doesn't resolve the issue. Do *not* use anything abrasive.
* Fuel Injectors: A clogged or faulty fuel injector in Bank 2 could prevent the correct amount of fuel from being delivered. This requires more advanced diagnostics, often involving injector flow testing.
* Fuel Pump: A weak fuel pump might not deliver enough fuel pressure, causing a lean condition, especially under load. Fuel pressure testing is necessary to confirm this.
* Fuel Pressure Regulator: A faulty regulator may allow too much fuel to return to the tank, leading to insufficient fuel pressure at the injectors.
* Oxygen Sensor (O2 Sensor): A faulty O2 sensor in Bank 2 can provide inaccurate readings to the ECU, causing it to adjust the fuel mixture incorrectly. This is less likely to be the primary cause of a P0174, but a bad sensor could exacerbate the problem.
* EGR Valve: A stuck-open EGR valve can introduce excess exhaust gases into the intake, creating a lean condition.
How to Fix It:
1. Visual Inspection: Start with a thorough visual inspection of all vacuum lines, the intake manifold, and the engine compartment for any obvious leaks or damage.
2. Check and Clean MAF Sensor: Carefully clean the MAF sensor with a MAF sensor cleaner.
3. Check the PCV Valve: Make sure the PCV valve is functioning correctly. It should be able to be easily pushed in and popped back out. If it's stuck, replace it.
4. Fuel Pressure Test: If vacuum leaks and MAF sensor issues are ruled out, have a fuel pressure test performed. This requires a fuel pressure gauge.
5. Injector Flow Test: If fuel pressure is good, an injector flow test may be necessary to assess the performance of the injectors in Bank 2.
6. O2 Sensor Check: While less likely the primary cause, you can check the Bank 2 O2 sensor. Often, a failing sensor will give slightly sluggish output, rather than total failure. A scan tool can help monitor the O2 sensor voltage to confirm proper function.
Important Considerations:
* Professional Diagnosis: If you're not comfortable performing these tests yourself, take your Cougar to a qualified mechanic for diagnosis and repair. A scan tool can provide more detailed information beyond the simple trouble code.
* Safety: Always disconnect the negative battery terminal before working on any electrical components or fuel system parts.
* Part Quality: When replacing parts, use high-quality replacement parts to prevent future issues.
This is not an exhaustive list, but covers the most common causes of a P0174 code. A systematic approach, starting with the easiest and most likely causes, is recommended. Remember to clear the trouble code after making repairs and test drive the vehicle to ensure the issue is resolved.
