* Brake Booster Hose: A leak here will severely impact engine performance, especially under load (like cruising at a steady speed). Check the hose connecting the intake manifold to the brake booster for cracks, splits, or loose connections. A failing booster will often lead to a soft brake pedal as well.
* EGR Valve Hose: The Exhaust Gas Recirculation (EGR) system impacts engine timing and fuel mixture. Leaks in the hoses connected to the EGR valve can cause hesitation, especially at cruising speeds. Inspect the hoses for cracks, kinks, or detachment from the valve and the intake manifold.
* MAP Sensor Hose: The Manifold Absolute Pressure sensor is crucial for the engine's computer to calculate fuel delivery. A leak in the hose connecting the MAP sensor to the intake manifold will throw off those calculations, leading to hesitation. This hose is usually a small-diameter hose, often located near the intake manifold.
* PCV Valve Hose: The Positive Crankcase Ventilation system helps prevent crankcase pressure buildup. While less likely to cause a direct hesitation at 50 mph, a severely clogged or leaking PCV system *can* contribute to rough running and performance issues. Check the hoses connected to the PCV valve.
* Intake Manifold Gaskets: While not strictly a "hose," leaks in the intake manifold gaskets are common and can cause vacuum leaks that manifest as hesitation or rough running, particularly under load. Inspect the gaskets visually for cracks or damage. This is often more involved than hose replacement.
How to Check the Hoses:
1. Visual Inspection: Start with a thorough visual inspection of all the vacuum hoses mentioned above. Look for cracks, splits, holes, or loose connections. Pay close attention to areas where the hoses bend or rub against other components.
2. Pressure Test (Advanced): For a more comprehensive diagnosis, a vacuum pressure test can pinpoint leaks. This requires a vacuum pump and gauge.
3. Start with the Easiest: Begin by checking the hoses that are easily accessible and visually inspect the others.
Important Considerations:
* Other Potential Causes: Vacuum leaks are a common cause of hesitation, but other problems could also be responsible (e.g., faulty fuel injectors, ignition system problems, mass airflow sensor issues). A vacuum leak is a good place to start because it's relatively inexpensive and easier to check than other potential problems.
* Professional Diagnosis: If you're uncomfortable inspecting and repairing vacuum hoses yourself, it's best to take your Malibu to a qualified mechanic for diagnosis and repair. A proper diagnostic scan may be necessary to pinpoint the exact problem.
Remember safety first! Always disconnect the negative battery terminal before working on any automotive system.
