Is Your 2025 Ford Mustang Stalling? Intake Leak & MAF Sensor Fix

The Basics

An intake manifold issue typically involves a vacuum leak, a faulty sensor, or a physical crack in the manifold itself. Based on 93 discussions, the core problem is unmetered air entering the engine, causing a lean fuel condition (often flagged by code P0171) and rough running. While aftermarket parts like the "weapon r intake manifold" are sometimes implicated, stock manifolds also fail due to age or heat cycling.

Symptoms

Owners consistently report these specific symptoms, often accompanied by diagnostic trouble codes (DTCs):

• Check Engine Light (CEL) with codes P0171 (System Too Lean) or P0301 (Cylinder 1 Misfire) being the most frequent triggers.
• Rough idle and stalling, especially when the engine is cold.
• Hissing or whistling sounds from the engine bay, indicating a vacuum leak.
• Poor acceleration and reduced power, as the engine computer struggles to correct the air/fuel mixture.
• In several cases, code P0446 (Evaporative Emission Control System Vent Control Circuit) appeared concurrently, suggesting a related vacuum issue affecting the EVAP system.

Common Causes

Analysis of successful fixes points to these primary culprits:

1. Vacuum Leaks (Most Common): Leaks occur at intake manifold gaskets, vacuum hose connections, or at the throttle body (TB) gasket. This is the first area to inspect.
2. Faulty Fuel Pressure Sensor: Code P0191 (Fuel Rail Pressure Sensor Performance) was directly linked to lean conditions in multiple cases. A bad sensor sends incorrect data to the engine computer.
3. Cracked or Warped Manifold: Plastic intake manifolds can crack, while aluminum ones can warp, creating leaks. This was noted specifically with some aftermarket manifolds.
4. Failed Intake Manifold Runner Control (IMRC) or related components: While not the top code, failures in systems that manage airflow inside the manifold can cause performance issues.

Repair Options

Start with the simplest, least expensive diagnostics before replacing major components.

1. Diagnose Vacuum Leaks (First Step):

   • Use a can of carburetor cleaner or propane. With the engine running, spray around the intake manifold gaskets, vacuum hoses, and throttle body. If the engine RPM changes, you've found your leak.
   • Cost: $10-$20 for cleaner. Success Rate: High for identifying the leak source.

2. Replace Intake Manifold Gaskets & Inspect Hoses:

   • If a leak is found at the manifold sealing surface, replacing the gaskets is the standard repair. Always inspect and replace any brittle or cracked vacuum hoses during this process.
   • Cost: $30-$100 for gasket sets. Difficulty: Moderate (requires manifold removal).

3. Test/Replace the Fuel Pressure Sensor:

   • If code P0191 is present, test the sensor's voltage and resistance against factory specifications. Replacing a faulty sensor resolved lean codes for several owners.
   • Cost: $50-$150 for the part. Difficulty: Low to Moderate.

4. Replace the Intake Manifold Assembly:

   • This is needed if the manifold itself is cracked or warped. Community reports suggest caution with certain aftermarket options, as fitment or quality issues can persist. Returning to an OEM manifold is often the most reliable fix.
   • Cost: $200-$600+ for the part, depending on OEM vs. aftermarket. Difficulty: High (involves disassembly of several components).

Shared Experiences

• "P0171 was my nightmare." A common thread: owners chased P0171 by cleaning MAF sensors and replacing O2 sensors, only to find the fix was a $40 set of intake manifold gaskets.
• The Aftermarket Caution: Multiple discussions mentioned ongoing drivability issues after installing a "weapon r" or similar intake manifold, leading owners to revert to OEM parts.
• The Multi-Code Puzzle: Several owners had simultaneous P0171 and P0446 codes. Fixing the intake manifold vacuum leak cleared both codes, highlighting how a single leak can affect multiple systems.
• Sensor vs. Source: One owner replaced the fuel pressure sensor (P0191) but the code returned. The root cause was a leaky manifold gasket causing low fuel rail pressure, demonstrating the importance of checking for leaks before condemning a sensor.

Price Breakdown

• DIY Repair (Gasket/Hose/Sensor Focus):
  • Parts: $30 - $200
  • Tools: Basic socket set, gasket scraper, torque wrench.
  • Total Range: $30 - $250. This covers the most common, successful fixes.
• DIY Repair (Full Manifold Replacement):
  • Parts: $200 - $600+
  • Total Range: $200 - $650.
• Professional Shop Repair:
  • Parts: $200 - $600+
  • Labor: 3-5 hours @ $100-$150/hr = $300 - $750
  • Total Range: $500 - $1,350+.
  • Recommendation: If you've confirmed a cracked manifold or lack DIY confidence, get a shop quote. Always ask them to verify the leak with a smoke test first.

Source Summary: This analysis is based on 93 owner discussions from Reddit and automotive forums.