2008-2015 Smart Fortwo Intake Manifold: Diagnosing Leaks, Rough Idle, and P0171 Codes
This guide covers the common failure symptoms, replacement costs, and what to inspect when buying a used intake manifold for your 451 chassis Smart Fortwo.
- The most common failure is a vacuum leak from a cracked plastic body or bad gasket, causing a rough idle, hissing noise, and a P0171 Check Engine Light code.
- New aftermarket manifolds are not readily available, making a quality inspected used OEM part the most practical and cost-effective solution.
- Owners of 2008-2009 models must verify the engine bay fire insulation recall (NHTSA 18V395000) has been performed for safety.
- Replacement is moderately difficult due to the tight engine bay, with total repair costs using a used part typically ranging from $375 to $710.
Symptoms of a Failing Intake Manifold
A bad intake manifold on a Smart Fortwo almost always fails by leaking. This allows unmetered air—air that the engine's computer doesn't know about—to enter the cylinders. This creates a "lean" condition (too much air, not enough fuel) and triggers several distinct symptoms.
1. Rough or Unstable Idle
This is the most common symptom. The engine may shake, sputter, or have an RPM that bounces up and down at a stoplight. The engine's computer struggles to maintain a steady idle with the incorrect air-fuel mixture caused by the leak.
2. Hissing or Sucking Noise from the Engine Bay
A distinct hissing or whistling sound, especially noticeable at idle, is a classic sign of a vacuum leak. This is the sound of air being sucked through a crack in the manifold's plastic body or through a failed gasket. The noise may change or get louder as the engine warms up.
3. Check Engine Light with Lean Codes
A vacuum leak will almost certainly trigger the Check Engine Light. The most common trouble code is P0171 - System Too Lean (Bank 1). This code specifically means the engine's oxygen sensor is detecting too much oxygen in the exhaust, confirming the lean condition caused by the unmetered air. You may also see misfire codes like P0300, P0301, P0302, or P0303.
4. Poor Acceleration and Loss of Power
When you press the gas, the engine may hesitate, feel sluggish, or lack its usual power. The incorrect air-fuel ratio prevents the engine from producing optimal power, making the car feel weak, especially when accelerating from a stop.
Important Safety Recall (2008-2009 Models): While not related to the intake manifold itself, a critical recall was issued for 2008-2009 Smart Fortwo models. The rear engine compartment insulation mat can degrade and contact hot exhaust components, creating a significant fire risk. There were 27 reported cases of engine fires related to this issue. Before performing any other repairs, ensure your vehicle has had this free recall service (NHTSA Campaign Number: 18V395000) completed by a dealer.
Buying a Used Intake Manifold: What to Check
Since new aftermarket intake manifolds for the 1.0L non-turbo Smart Fortwo are not readily available, a quality used OEM part is often the best and most cost-effective solution. A used original part guarantees perfect fitment and material quality compared to non-existent or unproven aftermarket options. Here’s what to inspect before you buy.
Physical Inspection Checklist:
- Check for Cracks: Carefully inspect the entire plastic body of the manifold, especially around the seams, mounting bolt holes, and where the runners meet the flange. Hairline cracks are the most common failure point.
- Inspect Gasket Surfaces: The gaskets that seal the manifold to the cylinder head are critical. On a used part, check that the gasket material isn't excessively flattened, brittle, or crumbling. While it's always best to install new gaskets, the condition of the old ones can tell you about the part's history.
- Verify All Ports and Nipples: Check that all small vacuum hose nipples are present and not broken off. A single broken nipple can render the entire manifold useless. Ensure any threaded sensor ports are not stripped.
- Confirm Part Numbers: Match the part number on the used manifold to your original part. Verified OEM numbers include 1320160532, A1320160432, A1320160532, and the Mitsubishi number 1540A162.
- Look for Internal Debris or Flashing: Look inside the runners. While rare, sometimes manufacturing defects like excess plastic "flashing" can break loose and cause issues. Ensure the inside is clean and free of debris.
Pro Tip: Many used manifolds are sold as an assembly with the throttle body and MAP sensor still attached. This can be a great value, giving you spare sensors for troubleshooting future problems.
Cost of Replacing the Intake Manifold
The cost can vary based on part choice and labor rates. Replacing the manifold is a moderately difficult job due to the tight confines of the Smart's engine bay.
| Part or Service | Estimated Cost | Notes |
|---|---|---|
| New OEM Manifold | $450 - $550+ | Sourced from a Mercedes-Benz/Smart dealer. A European parts site lists the part for over €400. |
| New Aftermarket Manifold | Not Widely Available | Complete aftermarket manifolds for this specific engine are not common, making this an unlikely option. |
| Used OEM Manifold | $75 - $160 | A cost-effective and reliable option found at online recyclers and eBay. |
| Shop Labor | $300 - $550 | Labor typically runs 2.5 to 4 hours. RepairPal estimates gasket replacement labor up to $412, with full manifold replacement being similar or slightly more. |
| Total (Used OEM + Shop Labor) | $375 - $710 | This represents the most common real-world repair cost. |
Replacement Overview & Difficulty
- Difficulty: 3.5 out of 5 (Moderate)
- Estimated Time: 2.5 - 4 hours
- DIY Feasible: Yes, for experienced DIYers.
Replacing the intake manifold requires working in a very tight space at the rear of the car. Accessing the mounting bolts (which may be T30 Torx) can be challenging. Some owners performing similar jobs have noted difficulty removing intake components without putting the engine into a 'service position' (lowering the subframe) or even having to cut the old plastic parts out. While it doesn't require highly specialized tools beyond a good socket set with extensions and Torx bits, patience and mechanical experience are essential.
Frequently Asked Questions (FAQ)
Can I just replace the intake manifold gaskets?
Yes, if you have confirmed the leak is from the gaskets and not a crack in the manifold itself. A shop can perform a smoke test to pinpoint the exact source of the leak. However, given the labor involved to remove the manifold, and the low cost of a good used unit, many people choose to replace the entire assembly to prevent future failure of the plastic body.
What is the difference between the intake manifold and the air intake box/resonator?
The intake system has several parts. The air filter box holds the filter. It connects via a large plastic tube or resonator to the throttle body. The intake manifold is the final component, located *after* the throttle body, which bolts directly to the engine's cylinder head to distribute the air.
Will a bad intake manifold cause my Smart car to not start?
It's possible, but less common. A very large vacuum leak can disrupt the air-fuel mixture so severely that the engine stalls immediately after starting or fails to start at all. More typically, it will start but run very poorly.
Do I need to do anything special after installing a new manifold?
No special programming or calibration is required after replacing the manifold itself. However, the engine computer will need to relearn its fuel adjustments. This usually happens automatically after driving for a few miles. You will also need to have the Check Engine Light codes cleared with a scan tool.
Technical Specifications
OEM Part Numbers: 1320160532 A1320160432 A1320160532 1540A162
Material: Plastic. Fits 1.0L (999cc) 3-cylinder non-turbocharged engine (Mitsubishi 3B21). For 451 chassis models only.
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- Smart Fortwo:
- Symptoms of a Failing Intake Manifold
- 1. Rough or Unstable Idle
- 2. Hissing or Sucking Noise from the Engine Bay
- 3. Check Engine Light with Lean Codes
- 4. Poor Acceleration and Loss of Power
- Buying a Used Intake Manifold: What to Check
- Physical Inspection Checklist:
- Cost of Replacing the Intake Manifold
- Replacement Overview & Difficulty
- Frequently Asked Questions (FAQ)
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