Why Your 2020 Subaru WRX Has a Bumpy Ride and Hard Shifts

How to Fix Throttle Body Issue

For owners of the 2020 Subaru WRX, throttle-related drivability issues can be frustrating and confusing. The symptoms often feel interconnected—a bumpy ride, erratic boost behavior, and shifting difficulties. Based on analysis of owner discussions, the root cause frequently traces back to the vehicle's Positive Crankcase Ventilation (PCV) system and its impact on manifold pressure. As one owner, MCXL, noted while discussing engine health, "I literally could go out and take this same video with all 3 of the healthy running vehicles on my property right now, one of which has a nearly new PCV system on it." This guide will walk you through diagnosing and resolving these throttle and pressure-related problems using data-driven solutions from the WRX community.

Symptoms

Owners of this turbocharged sedan report a specific cluster of symptoms that point toward a disruption in the engine's air management. The most common complaint is a bumpy or inconsistent ride, particularly during light throttle application or when coming on and off boost. This isn't just about road surface; it's a drivability issue where the power delivery feels jerky and unrefined. This sensation is often accompanied by noticeable hard shifting, especially between first and second gears, as the engine's power output and revs don't match driver input smoothly.

The core of these symptoms relates to charge pressure and vacuum leaks. The engine control module (ECM) relies on a precise balance of manifold pressure. When a fault like a compromised PCV valve or related gasket introduces an unmetered air leak, the ECU's calculations for fuel and boost are thrown off. This can cause the turbocharger to behave erratically—spooling inconsistently or not holding target boost—which owners perceive as a "charge pressure" problem. As one owner, T-pizzle, observed about throttle response, "Mine's always moved a little bit going on/off throttle, before and after shift stop installation." This subtle movement hints at the underlying pressure fluctuations.

Furthermore, these pressure inconsistencies can exacerbate the natural tendencies of the FA20DIT engine. The direct injection and twin-scroll turbo system can lead to specific behaviors during throttle lift-off. An owner, Capital-Yesterday798, theorized on this interaction: "My guess is the twin scroll turbo has a lot to do with it. That combined with direct injection creates fuel rich mixtures on throttle liftoff/shifting." When combined with a vacuum leak, these rich conditions or unexpected airflows can make the car feel mechanically unsound, leading to concerns about more serious mechanical issues.

Most Likely Cause

The primary cause of these throttle body and drivability issues in the 2020 WRX, as identified through owner reports and repairs, is a faulty Positive Crankcase Ventilation (PCV) valve or its associated gaskets and hoses. The PCV system is critical for managing crankcase pressure in the turbocharged FA20DIT engine. It routes blow-by gases (unburned fuel and air that slip past piston rings) back into the intake to be burned. A malfunctioning PCV valve—one that is stuck open, closed, or clogged—disrupts this delicate balance.

When the PCV system fails, it creates a vacuum leak. This leak is after the Mass Air Flow (MAF) sensor, meaning unmetered air is entering the intake manifold. The ECU has already calculated fuel delivery based on the air measured by the MAF sensor, so this extra air leans out the air/fuel mixture. The ECU then tries to compensate, often resulting in erratic idle, stumbling under load, and the "bumpy ride" owners describe. The leak also affects manifold absolute pressure (MAP) sensor readings, confusing the boost control system and leading to the reported "charge pressure" inconsistencies. This faulty valve can also allow excessive oil vapor into the intake, potentially coating the throttle body and intercooler, further degrading performance.

How to Diagnose

Diagnosing a PCV-related throttle issue requires a methodical approach, focusing on pressure tests and visual inspection. You will need a basic set of hand tools, a smoke machine (which can be rented or a simple homemade version), and an OBD-II scanner capable of reading live data.

Step 1: Scan for Codes and Check Live Data. Use your OBD-II scanner. You may not have a check engine light, but there could be pending codes like P0171 (System Too Lean) or P0300 (Random Misfire). More importantly, monitor live data. Key parameters are Long-Term Fuel Trim (LTFT) and Short-Term Fuel Trim (STFT). At idle, trims consistently above +10% indicate a vacuum leak. Also, watch the MAF sensor readings (g/s) and manifold pressure; erratic readings at steady throttle can point to a leak.

Step 2: Perform a Visual and Physical Inspection. With the engine cool, locate the PCV valve. On the FA20DIT, it's typically integrated into the rocker cover on the passenger side. Check the valve itself and all connected hoses, particularly the one running to the intake pipe. Look for cracks, brittleness, or oil saturation. Check the valve gasket where the PCV assembly meets the engine. Also, inspect the coolant pipes and intake hose connections near the throttle body for any signs of leakage or poor seals.

Step 3: Conduct a Smoke Test. This is the most definitive test. Introduce smoke into the intake system (usually via a vacuum port) with the engine off. Smoke escaping from the PCV valve housing, its gasket, or any of the connected hoses will pinpoint the leak. You can also perform a simple check: with the engine idling, carefully remove the oil fill cap. Some movement is normal, as MCXL explained, "It's normal for the oil cap to do that while the car is running. The case is under positive pressure while running." However, if it's extremely difficult to remove or there's a massive suction or blow-by, it indicates a blocked or failed PCV system.

Step-by-Step Fix

Replacing the PCV valve and related seals is a manageable DIY job. Allow 1-2 hours.

1. Gather Parts and Tools. Ensure you have the new PCV valve (often comes with a new gasket), and consider replacing the connecting hose. Have your socket set, torque wrench, pliers, and a new container for coolant if you need to move any pipes.
2. Disconnect the Battery. Always start by disconnecting the negative battery terminal for safety.
3. Remove the Intercooler. To access the PCV valve on the passenger-side rocker cover, you must remove the intercooler. Unclip the recirculation valve hose, loosen the clamps on the throttle body and turbo outlet, and carefully lift the intercooler out.
4. Access and Remove the PCV Valve. You will now see the PCV valve assembly mounted on the rocker cover. Disconnect the hose from the valve to the intake. Unbolt the valve assembly from the rocker cover (usually two 10mm bolts). Carefully remove the assembly, noting the old gasket.
5. Clean the Mounting Surface. Use a plastic scraper and brake cleaner to thoroughly clean the mating surface on the rocker cover. Ensure no old gasket material remains.
6. Install the New PCV Valve. Place the new gasket onto the new PCV valve assembly. Position it on the rocker cover and hand-tighten the bolts. Torque them to the factory specification (typically around 7-10 ft-lbs). Do not overtighten, as you can crack the rocker cover.
7. Reconnect the Hose. Attach the fresh or cleaned hose from the PCV valve to its port on the intake pipe. Ensure the clamp is tight.
8. Reinstall the Intercooler. Carefully place the intercooler back, ensuring the rubber couplers are seated properly on both the throttle body and turbo outlet before tightening the clamps. Reconnect the recirculation valve hose.
9. Reconnect the Battery.
10. Start the Engine and Test. Start the car and let it idle. Listen for any new hissing sounds. Use your OBD-II scanner to recheck fuel trims; they should begin to normalize after a short drive. Take the car for a test drive, focusing on low-throttle response and smoothness between gears. As one owner shared after addressing drivability concerns: "My rev matching is coming along decent (just recently had an ‘ooooh I see now’ moment... It’s been smoother that way)" — a sentiment that applies to the smoother operation post-repair.

Parts and Tools Needed

• Primary Part: PCV Valve Assembly. Subaru part number 11810AA310 (This is a common part for the FA20DIT; always verify with your VIN).
• Consumables: New PCV hose (Subaru part number 99071AC160 or equivalent silicone aftermarket hose), throttle body and intake cleaner.
• Tools: Socket set (10mm, 12mm, 14mm), torque wrench, flat-head and Phillips screwdrivers, pliers, plastic trim removal tools, OBD-II scanner.
• Diagnostic Tool: Smoke machine (professional or DIY version).

Real Owner Costs

The cost to fix this issue varies dramatically between DIY and shop repair, primarily due to labor.

• DIY Cost: Parts are relatively inexpensive. A genuine Subaru PCV valve assembly costs between $40 and $60. A new hose adds another $15-$30. If you need a smoke test, renting a professional tool might cost $50-$80 for a day. Total DIY investment: $55 to $170, depending on tools you need to acquire.
• Professional Repair Cost: At a dealership or independent shop, labor is the major factor. Diagnosis (often 1 hour of labor at $120-$180/hr) plus parts markup can add up. A typical repair bill for diagnosing a vacuum leak and replacing the PCV valve ranges from $300 to $600. If other intake gaskets or coolant pipes need attention, the cost can climb closer to $800.

Example: An owner paying a shop $450 for this repair could have spent under $100 in parts and an afternoon of their time. The savings are significant for a moderately skilled DIYer.

Prevention

Preventing a recurrence of this issue centers on routine maintenance and mindful driving.

1. Follow Severe Maintenance Schedules: If you drive aggressively or in stop-and-go traffic, consider changing your engine oil more frequently than the standard interval. Clean oil produces less harmful blow-by gunk that can clog the PCV valve.
2. Regular Visual Inspections: Every time you change your oil or have the intercooler off for any reason, take a moment to inspect the PCV hose for softness or cracks and check the valve gasket for oil seepage.
3. Use Quality Fuel and Oil: Top-tier gasoline and the correct weight of full-synthetic oil help keep combustion clean and minimize carbon deposits throughout the intake and PCV system.
4. Avoid Excessive Short Trips: Short trips where the engine doesn't fully warm up promote moisture and sludge buildup in the crankcase, which can accelerate PCV system contamination. As owners learning the manual transmission know, smooth operation is key: "I’ve been practicing driving at night so far as I transition from driving my automatic. I usually practice in the neighborhood and empty lots..." — similar patience with warm-up cycles helps engine health.

What Owners Say

Real experiences from SUBARU owners:

Owner Experiences

"Why so much throttle? I can make my Blizzaks break loose on snow/ice if I do that too." — VentiEspada (source)

"Edit: Added some context. I literally could go out and take this same video with all 3 of the healthy running vehicles on my property right now, one of which has a nearly new PCV system on it." — MCXL (source)

"It's normal for the oil cap to do that while the car is running. The case is under positive pressure while running. honestly try this on just about any modern car healthy or not and it will be similar." — MCXL (source)

Pro Tips from Owners

💡 "Straight piped the Q300 dual tip. Its loud, its mean, with a little throttle control while cruising can barely hear in cabin." — BuyWhole9350 (source)

Real Repair Costs

"I will keep my rant about the dealership not coming to the same conclusion after paying a $225 diagnostic fee to a minimum. Those of you who guessed the MAF sensor, take a shot of tequila as a reward." — toodrunktostand (source)

FAQ

Q: How long does it take to replace the PCV valve? A: For a first-time DIYer with basic tools, plan for 2 to 3 hours, accounting for intercooler removal and careful reassembly. An experienced mechanic familiar with the WRX can do it in about an hour.

Q: Can I drive my WRX with a suspected bad PCV valve? A: You can, but it's not advisable for the long term. Driving with a faulty PCV valve can lead to rough running, reduced fuel economy, and over time, oil sludge buildup or even premature wear on engine seals due to excessive crankcase pressure. Address it promptly.

Q: Is a bumpy ride and hard shifting a common issue on the 2020 WRX? A: Based on owner discussions, these specific symptoms linked to vacuum leaks and PCV faults are a known drivability concern. The turbocharged boxer engine is sensitive to unmetered air, making these symptoms noticeable when the PCV system fails.

Q: DIY vs mechanic—what's recommended for this fix? A: This repair is very suitable for a DIY enthusiast. The steps are straightforward, no specialized programming is required, and the cost savings are substantial. The main challenges are gaining access (intercooler removal) and ensuring no vacuum leaks are created upon reassembly. If you are uncomfortable with these tasks, a trusted mechanic is the way to go.

Q: Will a bad PCV valve cause my car to run rich and pop on deceleration? A: It can contribute. While some popping is characteristic of the direct-injection, turbocharged setup, as noted by an owner ("Literally on the stock exhaust you can get it to pop by aggressive shifting."), a significant vacuum leak from a bad PCV can create erratic fuel trims. This may exaggerate rich conditions on lift-off, potentially increasing exhaust pops or causing backfires.

Q: Do I need to clean the throttle body after fixing a PCV leak? A: It is highly recommended. A failing PCV valve often allows oil vapor to coat the intake tract. Once the leak is fixed, removing the intercooler provides perfect access to clean the throttle body plate and the intercooler itself, restoring optimal airflow.