Why Your 2020 Honda Fit is Misfiring and How to Clean the Intake Valves

How to Fix Valve Cover Replacement

For owners of the 2020 Honda Fit, addressing issues related to the valve cover often stems from a deeper, interconnected problem: carbon buildup on the intake valves. While a leaking valve cover gasket can cause oil leaks and mess, the owner data for this model year points overwhelmingly to symptoms caused by oil vapor being recirculated through the PCV (Positive Crankcase Ventilation) system, leading to deposits that disrupt engine operation. The fix isn't always a simple gasket swap; it involves diagnosing the root cause of the symptoms and often cleaning the intake valves. As one owner on FitFreak shared their diagnostic journey: "It sounds like you should have done the valve adjustment vs injectors. The valves almost never throw a code, but I'd swap back to the original injectors and clean the MAP sensor if you haven't yet."

Symptoms

Owners report a range of issues that initially seem disconnected but often trace back to problems in the valve train and intake system. The most common symptom is a rough idle and engine misfiring, particularly as mileage accumulates. This misfire can sometimes be severe enough to trigger a check engine light and put the vehicle into a limp mode, drastically reducing power. The engine may sound noisy or tick more than usual, which some owners mistake for needing a valve lash adjustment.

Another key symptom is excessive oil consumption or the presence of oil where it shouldn't be. While a classic valve cover gasket leak will leave oil on the top or side of the engine, the data suggests internal issues. Oil vapor being pulled through the PCV system can lead to carbon clogs on the back of the intake valves. This disrupts airflow and fuel mixture. As one owner noted regarding oil burning, "These motors shouldn't be burning oil, nor should any of course but any consumption especially at that rate I'd look into." You might also find the engine bay seems sweaty with oil mist, or the PCV valve itself becomes clogged.

Finally, performance issues like hesitation, lack of power, and poor fuel economy are frequently reported. These stem from the intake valves being coated in carbon deposits, preventing them from sealing properly and disrupting the precise air-fuel mixture needed for efficient combustion. The problem worsens over time, as noted by an owner asking, "I know carbon buildup is a thing that happens over time but how do you know when it’s time to service the valves?"

Most Likely Cause

The primary cause for the symptoms associated with "valve cover replacement" on this vehicle is carbon buildup on the intake valves due to PCV system operation. Unlike port fuel-injected engines where fuel cleans the back of the intake valves, the 2020 Honda Fit's direct-injection system sprays fuel directly into the cylinder. This means oil vapors from the crankcase, which are recirculated via the PCV valve to be burned, deposit directly onto the hot intake valves. Over time, these deposits accumulate, forming a thick, crusty layer of carbon.

This carbon buildup is the root of most reported issues. It disrupts airflow into the cylinder, leading to rough idling and misfires. It can prevent valves from closing fully, causing compression loss and a noisy valve train. It also interferes with the proper function of the MAP sensor, leading to incorrect fuel trims. A faulty or clogged PCV valve can accelerate this process by allowing excessive oil vapor into the intake. While a leaking valve cover gasket is a separate issue, the owner data strongly indicates that the internal consequences of the PCV system are a far more common culprit for the drivability symptoms owners experience.

How to Diagnose

Diagnosing this issue requires a methodical approach, starting with the simplest checks before moving to more invasive procedures. You'll need a basic set of hand tools, a code scanner (if the check engine light is on), and potentially a borescope.

First, scan for trouble codes. Codes like P0300 (random misfire) or specific cylinder misfire codes (P0301-P0304) are common. Also, check for fuel trim codes (P0171, P0174) indicating a lean condition, which can result from disrupted airflow due to carbon. Inspect the engine bay visually for obvious oil leaks from the valve cover gasket. Check the PCV valve by removing it and shaking it; it should rattle. If it's silent, it's clogged.

If basic checks don't reveal the issue, the next step is to inspect the intake valves. This requires removing the intake manifold. Once removed, you can use a flashlight to look into the intake ports. For a definitive view, use a USB borescope inserted through the port. You will be looking for black, crusty deposits on the back of the intake valves and the walls of the intake port. As one owner advised on the process, "When the valves are completely closed, you are not touching that portion of the valves that seal with the head. That's important... make sure you are at TDC for whatever cylinder's intake valves you are cleaning." Significant buildup confirms the diagnosis.

Step-by-Step Fix

The definitive fix for carbon-related drivability issues is a manual intake valve cleaning. Replacing a leaking valve cover gasket is a separate, simpler procedure. Here is the process for cleaning the intake valves, which addresses the core problem identified by owners.

1. Disconnect the Battery: Always start by disconnecting the negative battery terminal for safety.
2. Remove the Intake Manifold: This involves removing the air intake assembly, disconnecting all vacuum lines, electrical connectors (like the MAP sensor and fuel injectors), and unbolting the manifold from the cylinder head. Keep track of all bolts and gaskets.
3. Secure Valves and Prepare: Rotate the engine by hand (using a socket on the crankshaft pulley bolt) to close the intake valves for the cylinder you are working on. This prevents debris from falling into the cylinder. As owner 't-rd' emphasized, ensuring the valves are closed is critical.
4. Apply Cleaner and Agitate: Soak the carbon deposits with a dedicated intake valve cleaner or brake cleaner. Let it sit for several minutes to soften the deposits. Then, use a specialized tool to scrape the carbon away. Owners have used various methods: "I used a long pick with a spoon shape tip, not a pointy tip. The carbon deposit is soft once you soak it with cleaner + brake clean, easy to scrape off." Another described their toolkit: "I used the combo of brake cleaner + CRC intake valve cleaner + bunch of towels + a long pick."
5. Scrape and Wipe Clean: Gently scrape the softened carbon off the valve and port walls. Use lint-free towels to wipe away the sludge. Repeat the soak-and-scrape process until the metal is clean. Be meticulous and avoid letting large chunks fall into the cylinder.
6. Consider Advanced Tools: For a more thorough job, some owners invest in a walnut blaster. This uses crushed walnut shells as a mild abrasive to blast carbon away. "Fwiw if you can access a walnut blaster the finnegaling around in the valves is a world of difference. I tried the zip tie method and it was bad enough I bought a blaster," shared one owner. However, the cost is a barrier: "I do not have a $400 walnut blaster + intake port adapter to do it easily."
7. Clean All Ports: Move the engine to close the valves on the next cylinder and repeat the cleaning process for all four intake ports.
8. Reinstall and Replace: Before reinstalling the intake manifold, replace the intake manifold gasket and the PCV valve. This is a crucial preventative step. Reinstall all components in reverse order, ensuring all connections are tight.
9. Reconnect Battery and Test: Reconnect the battery, start the engine, and let it idle. It may run rough initially as remaining cleaner burns off. Take it for a test drive to ensure the misfires and hesitation are resolved.

Parts and Tools Needed

• Intake Manifold Gasket: Essential for re-sealing. Honda part number is often 17171-R5G-003 (confirm for your specific VIN).
• PCV Valve: A new valve prevents rapid re-accumulation of carbon. Honda part number is typically 17130-R5G-003.
• Valve Cover Gasket Set: If you have a confirmed external leak. Includes spark plug tube seals. Honda part number 12341-R5G-000 for the gasket.
• Cleaning Chemicals: CRC Intake Valve Cleaner, brake cleaner, or a similar product.
• Tools: Basic socket set, torque wrench, long pick or dental-style scraping tools, lint-free shop towels, flashlight or borescope.
• Optional/Advanced: Walnut blaster kit (e.g., from DIY brands) with appropriate intake port adapters. As noted, this can cost around $400.

Real Owner Costs

The cost to address this issue varies dramatically between DIY and professional service, and depends on the method used.

• DIY Manual Cleaning: This is the most cost-effective route. Parts (PCV valve, intake manifold gasket) will cost under $50. Cleaning chemicals and basic tools might add another $30-$50. The primary cost is your time, which can be 4-8 hours for a first-timer. Total out-of-pocket: $80 - $100.
• DIY with Walnut Blaster: If you invest in the equipment for a more professional result, your cost jumps. The blaster kit alone is ~$400. Adding parts, your total DIY cost could be $450 - $500. However, you own the tool for future cleanings.
• Professional Service: Taking your car to a dealership or independent shop for a "carbon cleaning" or "induction service" is expensive. While owners didn't quote exact prices for the Fit, industry standard for this service on direct-injection engines typically ranges from $600 to $1,200+, depending on labor rates and the method used (chemical vs. walnut blasting). The higher end reflects the more effective walnut blasting procedure.

Prevention

Preventing severe carbon buildup is challenging on direct-injection engines but not impossible. The most effective preventative measure is installing an oil catch can in the PCV system. This device intercepts oil vapor before it can reach the intake manifold, significantly reducing the rate of deposit formation. Regularly inspecting and replacing the PCV valve (every 30,000-60,000 miles) is also crucial. Using high-quality, low-volatility synthetic engine oil, as one owner found success with, can help: "My RMS started leaking before 130,000 mi and I switched to Mobil 1 EP High Mileage, solved the issue." While not a cure-all, it may reduce the amount of vapor produced. Finally, occasional use of a Top Tier detergent gasoline can help keep the combustion chamber and fuel injectors clean, offering minor indirect benefits.

What Owners Say

Real experiences from HONDA owners:

Owner Experiences

"i bought a fumoto valve for my 2020 wrx a few oil changes ago (the original one F-108), had tried to thread it on but it interfered with the oil pan lip. got a 1/2" adapter and tried that on the next oil change, but it still wasn't long enough and interfered." — thejesterthejester (source)

"These motors shouldn't be burning oil, nor should any of course but any consumption especially at that rate Id look into. My RMS started leaking before 130,000 mi and I switched to Mobil 1 EP High Mileage, solved the issue." — 2015LXFIT (130,000 miles) (source)

"Fwiw if you can access a walnut blaster the finnegaling around in the valves is a world of difference. I tried the zip tie method and it was bad enough I bought a blaster." — 2015LXFIT (source)

Pro Tips from Owners

💡 "I used a long pick with a spoon shape tip, not a pointy tip. The carbon deposit is soft once you soak it with cleaner + brake clean, easy to scrape off." — t-rd (source)

💡 "It sounds like you should have done the valve adjustment vs injectors. The valves almost never throw a code, but I'd swap back to the original injectors and clean the MAP sensor if you haven't yet." — newengland72 (source)

💡 "When the valves are completely closed, you are not touching that portion of the valves that seal with the head. That's why it's important you open up the valve cover and make sure you are at TDC for whatever cylinder's intake valves you are cleaning." — t-rd (source)

Real Repair Costs

"I do not have a $400 walnut blaster + intake port adapter to do it easily. I used the combo of brake cleaner + CRC intake valve cleaner + bunch of towels + a long pick." — Gekisen (source)

FAQ

Q: How long does it take to clean the intake valves? A: For a DIYer doing it for the first time, budget a full day (6-8 hours). This includes time to carefully remove the intake manifold, the meticulous cleaning process itself, and reassembly. Experienced individuals can cut this time in half. As owner 't-rd' noted, "Most of the time is spent waiting for fluid to soak and softening up the carbon deposits, then pick scraping and wiping."

Q: Can I drive my car with carbon-clogged intake valves? A: You can, but you shouldn't for long. Performance will suffer with misfires, poor fuel economy, and lack of power. In severe cases, a chunk of carbon can break off and cause catastrophic engine damage by getting stuck between a valve and its seat. It's best to diagnose and address the issue promptly.

Q: Is carbon buildup a common issue on the 2020 Honda Fit? A: Yes, based on owner discussions, it is a known and relatively common issue for the L-series direct-injection engine in this generation. It is not a design flaw unique to Honda but a characteristic of most gasoline direct-injection (GDI) engines without supplemental port fuel injection.

Q: DIY vs mechanic - what's recommended for this job? A: This is a classic intermediate DIY job. It requires patience and mechanical aptitude but not exotic tools (unless walnut blasting). If you are comfortable with tasks like changing spark plugs and following detailed instructions, you can save hundreds of dollars. If the thought of removing the intake manifold is daunting, or you lack the time, then paying a professional is the better choice. The key is ensuring they perform a physical cleaning (walnut blasting is best), not just a chemical "pour-in" treatment, which is less effective for heavy buildup.

Q: Will replacing the valve cover gasket fix my misfire? A: Almost certainly not. A valve cover gasket leak is an external oil leak. While a severe leak could allow oil to foul spark plugs, the misfires discussed by owners are overwhelmingly caused by internal carbon buildup on the valves. Replacing the gasket will only stop oil from dripping on your driveway.

Q: How often should the intake valves be cleaned? A: There's no fixed schedule, but owners start reporting symptoms typically between 60,000 and 100,000 miles. If you install an oil catch can, you may extend this interval significantly. Using a borescope for inspection every 30,000-40,000 miles after 60,000 miles is a good proactive practice.