OBD-II Code P2191: System Too Lean at Higher Load (Bank 1)

What Does P2191 Mean?

The Engine Control Module (ECM) detects that Bank 1 of the engine receives too much air and insufficient fuel specifically during high power demand (accelerating, merging, or climbing). The computer injects maximum fuel to compensate—often reaching a +25% fuel trim limit—but the lean condition persists under load.

Technical definition: The SAE/OBD-II definition is "System Too Lean At Higher Load Bank 1". The powertrain control module (PCM) detects through the Bank 1 primary oxygen (O2) or air-fuel ratio sensor that the air-fuel mixture is excessively lean when the engine operates under significant load. The code sets when long-term fuel trim adjustments max out, yet the sensor still reports excess oxygen in the exhaust.

Can I Drive With P2191?

Yes, But With Caution. You can drive short distances, but you must avoid heavy acceleration, towing, or climbing steep hills. Ignoring this code causes severe engine hesitation, misfires, and elevated combustion temperatures that permanently damage pistons, exhaust valves, and the catalytic converter. Continuing to drive under heavy load turns a moderate repair into a catastrophic one, adding $1,200 to $2,800 for a new catalytic converter.

Common Causes

• Vacuum Leaks & PCV System Failures (Very Common) — A cracked intake manifold, broken vacuum hose, or a stuck-open PCV valve allows unmetered air into the engine. While the ECM compensates at idle, the massive influx of unmetered air during acceleration overwhelms the fuel trim limits, triggering the code.
• Clogged or Faulty Fuel Injectors (Very Common) — Carbon deposits restrict fuel injectors on Bank 1, preventing them from delivering the required fuel volume during high-demand situations. This is exceptionally common on Gasoline Direct Injection (GDI) engines.
• Low Fuel Pressure (Pump or Filter) (Common) — A weak fuel pump or clogged fuel filter fails to supply adequate fuel volume during acceleration. Pressure reads normal at idle but drops drastically under load, starving the engine.
• Dirty or Faulty Mass Air Flow (MAF) Sensor (Common) — Dirt or oil on the MAF sensor's delicate wire causes it to under-report actual airflow. The ECM calculates insufficient fuel delivery, creating a lean condition that peaks when airflow is highest.
• Faulty Front Oxygen (O2) Sensor (Less Common) — An old or contaminated Bank 1 primary O2 sensor sends a false 'lean' signal to the computer. The ECM maxes out fuel trims trying to fix a problem that doesn't exist.
• Exhaust Leaks Before the O2 Sensor (Less Common) — A cracked exhaust manifold pulls outside air into the exhaust stream. The O2 sensor detects this extra oxygen and incorrectly reports a lean condition.
• Contaminated Fuel (Rare) — Gasoline with high water content or excessive ethanol (like E85 in a standard engine) alters combustion properties, creating a lean condition the fuel system cannot compensate for.

Symptoms

• Significant Loss of Power Under Load — The vehicle hesitates, stumbles, or feels exceptionally weak when merging onto a highway or climbing a hill.
• Check Engine Light Illuminated — The Malfunction Indicator Lamp (MIL) turns on, typically immediately following a high-load acceleration event.
• Engine Misfires or Rough Running — A shudder or vibration occurs under load as the lean mixture fails to ignite, often triggering secondary misfire codes (P0301-P0304).
• 10-20% Drop in Fuel Economy — Miles-per-gallon (MPG) plummets because the ECM commands maximum fuel enrichment in a desperate attempt to correct the lean condition.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this code.

Common Fixes & Costs

• Repairing a Vacuum Leak or PCV System — Parts: $20-$150, Labor: $125-$400, ~2.5 hr book time (DIY)
• Cleaning or Replacing the MAF Sensor — Parts: $10-$250, Labor: $50-$150, ~0.5 hr book time (DIY)
• Replacing Clogged Fuel Injectors — Parts: $50-$350, Labor: $200-$500, ~2.5 hr book time (Intermediate)
• Replacing the Fuel Pump Assembly — Parts: $250-$700, Labor: $250-$500, ~3.0 hr book time (Professional)

DIY vs Professional

• Cleaning the Mass Air Flow (MAF) Sensor — Beginner:
  Tools: Screwdriver/socket set, MAF Sensor Cleaner spray.
• Replacing a PCV Valve/Hose — Beginner:
  Tools: Pliers, screwdriver, socket set.
• Replacing Fuel Injectors — Beginner:
  Tools: Socket set, torque wrench, fuel line disconnect tools, new O-rings, lubricant.
• Replacing an Intake Manifold Gasket — Beginner:
  Tools: Extensive socket set, torque wrench, scrapers, coolant drain pan, shop vacuum.
• Replacing an In-Tank Fuel Pump — Beginner:
  Tools: Fuel tank removal tools, fuel line disconnect tools, new lock ring.

Used vs. New Parts: Buying Guide

When a used part is worth it: Buy used for high-cost, low-wear electronic components like an Engine Control Module (ECM) or a complete intake manifold assembly. Never buy used mechanical wear items like fuel pumps or fuel injectors.

Donor-vehicle mileage cap: roughly under 80000 miles for the part to have meaningful remaining life.

Donor quality checklist:

• Verify the part number exactly matches the original.
• Check the donor vehicle's history to ensure it wasn't scrapped for a fuel or engine fire.
• Obtain at least a 90-day warranty.

Decision logic:

• If The part is a known wear item like a fuel pump or fuel injector. → Buy new. The risk of premature failure is high, and repeat labor costs outweigh initial savings.
• If The part is electronic (MAF sensor, ECM) and an OEM new part exceeds $400. → Buy a used OEM part. Quality is more consistent than cheap aftermarket alternatives.
• If The part is a mechanical seal like a PCV hose or intake gasket. → Always buy new. These degrade with age and heat.

Warranty tradeoff: Used parts carry a 30-90 day functional warranty. New aftermarket parts offer 1-year to lifetime warranties. New OEM parts offer a 1-year manufacturer-backed warranty.

Worst-case if a used part fails: $400-$1,500 if a used fuel pump fails, requiring repeat labor and a second replacement part.

What Happens If You Wait — Timeline

1. 0-1 month: Check Engine Light illuminates. Slight hesitation occurs during hard acceleration. The issue is intermittent. (MPG impact: 5-10%% · Added cost: $20-$50 in wasted fuel)
2. 1-4 months: Hesitation under load becomes consistent. The engine misfires when climbing hills. Elevated combustion temperatures begin stressing the catalytic converter. (MPG impact: 10-20%% · Added cost: $50-$200 in wasted fuel)
3. 4-8 months: Sustained high temperatures melt the internal substrate of the catalytic converter. The engine feels severely underpowered. (MPG impact: 15-25%% · Added cost: $1,200-$2,800 for a mandatory catalytic converter replacement)
4. 8+ months: Catastrophic failure. The melted catalytic converter clogs the exhaust, making the car undrivable. Fragmented substrate gets sucked back into the engine, destroying pistons and valves. (MPG impact: 25%+% · Added cost: $3,000-$7,000 for engine rebuild and exhaust replacement)

Cost of Not Fixing It

• 0-1 month: Noticeable loss of power during acceleration, a 10-15% drop in fuel economy, and engine hesitation under load. (Added cost: $20-$50 in wasted fuel.)
• 1-6 months: Elevated combustion temperatures overheat and melt the catalytic converter substrate, causing irreversible failure. (Added cost: $1,200-$2,800 for catalytic converter replacement.)
• 6+ months: Severe internal engine damage. Persistently high temperatures burn exhaust valves and damage pistons. A fragmented catalytic converter sends debris back into the engine. (Added cost: $3,000-$7,000 for engine rebuild or replacement.)

Diagnosis Steps

1. Analyze Live Data & Fuel Trims Under Load
   Use an advanced scanner to graph Short-Term (STFT) and Long-Term Fuel Trim (LTFT) for Bank 1. Recreate the high-load condition while driving. If LTFT maxes out (typically > +20%) while STFT climbs, the PCM sees a severe lean condition and cannot compensate. Normal total fuel trim (STFT + LTFT) must not exceed +/- 10%.
   Tools: Advanced OBD-II Scanner (Advanced)
2. Clean and Test the MAF Sensor
   Remove the MAF sensor and spray the element with dedicated MAF cleaner. Never touch the wire. Reinstall after it air-dries. Using a scan tool, monitor the MAF sensor g/s reading. A 2.0L engine should read 2-7 g/s at idle and rise smoothly to 15-25 g/s at 2500 RPM. Lower readings indicate a faulty sensor.
   Tools: Screwdriver/Ratchet set, MAF Sensor Cleaner, Advanced OBD-II Scanner (Beginner)
3. Perform an Intake Smoke Test
   Force low-pressure, vaporized mineral oil into the intake system using a smoke machine. Smoke pouring from cracked hoses, intake manifold gaskets, or the PCV valve instantly reveals the source of unmetered air.
   Tools: Automotive Smoke Machine (Intermediate)
4. Test Fuel Pressure Under Load
   Connect a fuel pressure gauge. Check pressure at idle, then safely increase engine RPM to 3000 RPM under load. Pressure must meet manufacturer specs (e.g., 30-45 PSI for Port Injection, 500+ PSI for GDI) and must not drop. A pressure drop confirms a weak fuel pump or clogged filter.
   Tools: Fuel Pressure Gauge Kit (PFI & GDI compatible) (Advanced)
5. Test Fuel Injectors
   Measure resistance across each Bank 1 injector terminal with a multimeter (standard is 10-16 ohms). Readings must be within 0.5 ohms of each other. For a definitive diagnosis, use a bidirectional scanner to perform an injector balance test, or remove them for professional flow testing.
   Tools: Multimeter, Advanced OBD-II Scanner (Advanced)
6. Test O2 Sensor Response
   Introduce unlit propane into the intake stream while the engine idles. Watch live O2 sensor data. Bank 1 Sensor 1 voltage must instantly spike high (towards 0.9V). If the reading remains low or reacts sluggishly, the sensor is 'stuck lean' and requires replacement.
   Tools: Advanced OBD-II Scanner, Propane Torch (unlit) (Advanced)
7. Inspect Spark Plugs
   Remove Bank 1 spark plugs. A lean condition leaves a white, blistered, or ashy deposit on the insulator. If only one plug shows these signs, the corresponding fuel injector is clogged.
   Tools: Ratchet Set, Spark Plug Socket (Intermediate)

When This Code Triggers (Freeze-Frame Conditions)

• Engine Coolant Temp: 180-200°F (82-93°C) (The engine is fully warmed up; the code does not set on a cold engine.)
• Engine RPM: 1500-3200 RPM (The engine operates above idle, typically during steady cruising or moderate acceleration.)
• Engine Load: 30-60% (The fault triggers during significant power demand, though not necessarily at wide-open throttle.)
• Vehicle Speed: 35-65 mph (The code sets during highway driving, merging, or climbing a grade.)

Related Codes

• P0171 — P0171 means 'System Too Lean (Bank 1)' at any time. P2191 specifies the lean condition happens under load. Having both strongly points to a fuel delivery failure (pump/filter) rather than a minor vacuum leak.
• P2096 — 'Post Catalyst Fuel Trim System Too Lean'. Confirms the lean condition is severe enough that unburned oxygen is passing completely through the catalytic converter.
• P0300-P0308 — Misfire codes. If P2191 pairs with a specific cylinder misfire (e.g., P0301 for cylinder 1), the fuel injector for that exact cylinder is clogged or dead.
• P2193 — 'System Too Lean at Higher Load (Bank 2)'. If both banks run lean simultaneously, the cause is a central component like the fuel pump, fuel filter, or MAF sensor, not a single bad injector.

Climate & Environmental Factors

• Cold Weather: Freezing temperatures cause plastic intake manifolds and rubber vacuum hoses to contract, opening up micro-cracks. This creates severe vacuum leaks that trigger P2191 on cold mornings but seemingly disappear once the engine warms and expands.
• High Altitude: Reduced air density at high altitudes forces the ECM to adjust fueling. If a borderline issue exists (like a slightly weak fuel pump), the altitude change pushes fuel trims past the failure threshold, triggering the code.

How to Talk to a Mechanic About This Code

Say this: "I have a P2191 code, 'System Too Lean at Higher Load,' and I'm experiencing hesitation during acceleration. Please start by checking long-term fuel trims under load, perform a smoke test for vacuum leaks, and verify fuel pressure at 3,000 RPM."

This proves you understand the code is load-dependent. It forces the mechanic to test fuel delivery and vacuum integrity rather than blindly replacing an expensive oxygen sensor.

Avoid saying:

• 'My check engine light is on, can you look at it?'
• 'The code says it's an oxygen sensor, can you replace it?'
• 'Just fix whatever you think is wrong.'

Questions to ask before authorizing the repair:

• What were the long-term fuel trim values for Bank 1 when you put the engine under load?
• Did the smoke test reveal any vacuum leaks? If so, exactly where?
• What was the fuel pressure reading at idle versus at 3,000 RPM under load? Did it drop?
• Will you provide a printout of the freeze-frame data and the final diagnostic report?
• What is the warranty on this specific repair, covering both parts and labor?

Where to Take It: Dealer vs Independent vs Chain

• Dealer: Use only if your vehicle has a known TSB for P2191 or is under warranty. Otherwise, avoid.
  Best for: Vehicles under powertrain or emissions warranty., Known manufacturer TSBs (e.g., Hyundai/Kia fuel pumps, GM PCV issues)., Complex software issues requiring an ECM reflash.
  Downsides: Labor rates are 50-100% higher than independent shops., Dealers replace entire assemblies (full intake manifolds) instead of $20 gaskets. (Typical cost: +50% vs. baseline)
• Independent Shop: The best overall choice. They offer the right balance of diagnostic expertise and reasonable labor rates.
  Best for: Out-of-warranty vehicles., Standard diagnostics like fuel pressure tests and smoke tests., Cost-effective gasket and sensor replacements.
  Downsides: Diagnostic equipment quality varies. Ensure they own a smoke machine and advanced bidirectional scanner. (Typical cost: +0% vs. baseline)
• Chain Shop: Avoid for diagnosis. Acceptable only if you have already pinpointed the exact part that needs replacing.
  Best for: Simple, pre-diagnosed parts replacement like swapping a MAF sensor.
  Downsides: Technicians lack experience with load-dependent lean diagnostics., High pressure to upsell unnecessary fuel system flushes or O2 sensors. (Typical cost: -10% vs. baseline)

When to Walk Away From the Repair

If the total estimated repair cost for P2191 exceeds 50% of your car's current private-party value, sell the vehicle as-is.

• Car worth $4500, fix is $2500: Walk away. The repair cost (likely a fuel pump and catalytic converter) is over half the car's value.
• Car worth $12000, fix is $850: Fix it. The repair cost is well under the threshold and restores full vehicle performance.
• Car worth $2500, fix is $1500: Walk away. The repair is not economically viable.

What Scan Tool You Need for This Code

Minimum: A scanner that displays live data graphing for Long-Term Fuel Trims (LTFT), O2 sensor voltage, and MAF sensor readings (g/s).

A $20 code reader only shows the P2191 code. It cannot display the live fuel trims required to prove the engine is starving for fuel under load, leading to blind parts replacement.

Budget: Bluetooth OBD2 Adapter with Torque Pro App (~$30) — Graphs live fuel trims, O2 data, and MAF readings on your smartphone while driving, proving if the lean condition is load-dependent.

Mid-range: Foxwell NT510 Elite (~$180) — Provides manufacturer-specific live data and bidirectional controls to command the fuel pump on and off during testing.

Professional: Autel MaxiCOM MK808S (~$500) — Offers full bidirectional control to perform automated injector balance tests and guided fuel pressure diagnostics.

Rent vs buy: For a one-time fix, use AutoZone's Loan-A-Tool program to rent a scanner for free. Buy a midrange scanner if you perform your own maintenance.

How to Clear the Code After You Fix It

1. Use an OBD-II scan tool to clear the fault codes.
2. Perform a complete OBD-II drive cycle to allow readiness monitors to run.

Drive cycle (~30 minutes): Start the engine cold and idle for 3 minutes. Drive in mixed city/highway conditions, including steady cruising between 45-60 mph for 10 minutes. Perform 3-5 moderate accelerations. Allow the vehicle to cool completely (8 hours) and repeat.

Readiness monitors affected: Catalyst (CAT) Monitor, Oxygen (O2) Sensor Monitor, Evaporative (EVAP) System Monitor

Before emissions retest: drive at least 100 miles to fully set monitors.

Watch out for:

• Clearing the code without fixing the root cause guarantees the code returns within 50 miles.
• Clearing the code resets readiness monitors. The vehicle automatically fails an emissions test until driven 50-100 miles to reset them.

Will This Fail Emissions / State Inspection?

Yes — this code typically fails an OBD-II emissions inspection.

• California: An active P2191 code is an automatic smog check failure. After repair, all OBD-II readiness monitors must read 'Ready', requiring 100+ miles of driving before a re-test.
• New York: The NYS DMV emissions inspection includes an OBD-II scan. A Check Engine Light with code P2191 results in immediate failure.
• Texas: In the 17 Texas counties requiring emissions testing, a vehicle with P2191 fails the OBD-II portion of the annual safety inspection.

Most Commonly Affected Vehicles

• Hyundai Sonata, Elantra, Veloster, Tucson (2011-2018) — Extremely common due to failing high-pressure fuel pumps (HPFP) or clogged injectors on GDI engines. Check for active TSBs requiring fuel pipe replacement and ECM software updates.
• Kia Optima, Soul, Sportage, Forte (2012-2020) — Shares GDI platforms with Hyundai. A fuel pressure test under load is mandatory before replacing any sensors.
• Ford F-150, Explorer, Mustang (2011-2021) — Frequently triggered by vacuum leaks from cracked plastic intake manifolds or failed purge valves. Perform a smoke test before replacing EcoBoost fuel components.
• Chevrolet Cruze, Equinox, Malibu (2010-2017) — A clogged PCV orifice inside the intake manifold creates a massive vacuum leak on 1.4L and 2.4L Ecotec engines. GM issued Special Coverage 14882 to drill out the blockage.
• Volkswagen Jetta, Golf, Passat, Tiguan (2010-2019) — Linked heavily to cracked PCV valve assemblies or failing high-pressure fuel pumps on TSI/FSI direct-injection engines.
• Mazda 3, 6, CX-5 (2012-2018) — Caused by dirty MAF sensors and severe carbon buildup on the intake valves of Skyactiv GDI engines, which disrupts airflow.

Manufacturer-Specific Notes

• Hyundai/Kia: Certain GDI engines have extended 15-year/150,000-mile warranties covering connecting rod bearing failure, which can result from severe lean conditions. Always check your VIN with a dealer for active campaigns.
• Ford: TSB 23-2194 addresses engine block porosity leaks on 2022-2023 5.0L F-150s, requiring intake gasket replacement. Smoke testing is mandatory on Ford plastic manifolds before diagnosing fuel issues.
• Chevrolet (GM): On 1.4L/2.4L Ecotec engines, P2191 is caused by a clogged PCV orifice inside the intake manifold. The fix requires removing the manifold and physically drilling out the blockage.
• Mazda: Skyactiv engines suffer from extreme carbon buildup on the back of intake valves. This disrupts airflow into the cylinders, causing load-dependent lean conditions that require walnut blasting to fix.

Real Owner Stories

2014 Kia Optima at 175K miles

Check Engine Light illuminated with code P2191. MPG dropped to 18, but no significant loss of power was noticed.

What they tried:

1. Replaced O2 sensor with a cheap aftermarket part, triggering new codes (P2096, P0451).
2. Replaced EVAP sensor and gas cap.
3. Replaced O2 sensor again with an OEM Denso part, clearing secondary codes but P2191 remained.

Outcome: A mechanic diagnosed a faulty PCV valve. Replacing the PCV valve resolved the vacuum leak and cleared the code permanently for $130.

Lesson: Never assume the sensor reporting the code is the broken part. A $20 PCV valve creates vacuum leaks that mimic sensor failures. Avoid cheap aftermarket sensors.

2017 Kia Soul at 140K miles

Car broke down after accelerating from a stop. An auto parts store previously diagnosed the intermittent Check Engine Light as a bad O2 sensor.

What they tried:

1. A shop replaced the fuel pump after the breakdown.

Outcome: Code P2191 returned immediately after the fuel pump replacement, and the car still hesitated under load. The root cause (clogged injectors) was ignored.

Lesson: A breakdown is a symptom, not the root cause. P2191 requires testing fuel pressure under load and checking injector flow before firing the parts cannon at the fuel pump.

2017 Hyundai Elantra GT

Car was difficult to start and ran rough when cold, triggering P2191.

What they tried:

1. Replaced a dirty air filter with no success.
2. Prepared to buy a new MAF sensor and fuel injectors.

Outcome: The owner discovered the tank was accidentally filled with E85 fuel. Draining the tank and refilling with regular gasoline instantly resolved the issue.

Lesson: Always evaluate recent events. If a code appears immediately after refueling, contaminated or incorrect fuel is the most likely culprit.

2013 Kia Sportage with recent engine replacement

Code P2191 appeared immediately after Kia replaced the engine under a recall. The car idled rough and got poor gas mileage.

What they tried:

1. Dealership replaced the intake manifold gasket, but the code returned.
2. Owner checked live data: Long-Term Fuel Trims were maxed out at +28%.

Outcome: A smoke test revealed a disconnected vacuum hose behind the intake manifold, left off during the engine swap.

Lesson: If a code appears immediately after a major repair, the mechanic caused it. A disconnected hose or pinched gasket is almost guaranteed.

How to Prevent This Code From Triggering

• Use Top-Tier rated gasoline (Every fill-up) — Top-Tier gasoline contains high detergent concentrations that prevent carbon deposits from clogging fuel injectors.
• Clean the Mass Air Flow (MAF) sensor (Every 30,000 miles) — Removes oil fumes and dust from the sensor wire, ensuring the ECM calculates the exact air-fuel ratio required under load.
• Replace the fuel filter (Every 60,000 miles) — Ensures the fuel pump delivers maximum pressure and volume during heavy acceleration, preventing load-dependent lean conditions.
• Perform a professional fuel system cleaning (Every 45,000 miles (GDI engines)) — Ultrasonic cleaning removes baked-on carbon from direct injectors, restoring proper spray patterns and fuel volume.
• Inspect PCV and vacuum hoses (Annually) — Catches brittle, cracking rubber hoses before they split open and create massive unmetered air leaks.

Frequently Asked Questions

What does 'Bank 1' mean?

Bank 1 is the side of the engine containing cylinder number 1. On an inline 4-cylinder engine, there is only one bank. On a V6 or V8, it is typically the side with the cylinder furthest forward in the engine bay.

What are the most common misdiagnosis mistakes for P2191?

The most common mistake is immediately replacing the oxygen sensor because it reports the lean condition. The O2 sensor is usually functioning correctly. A proper diagnosis requires testing fuel pressure under load and performing a smoke test for vacuum leaks.

Why does this code only appear when I accelerate hard?

At idle, fuel demand is low, allowing the ECM to compensate for a weak fuel pump or small vacuum leak. During acceleration, the engine requires a massive, instant volume of fuel and air. If the fuel pump cannot keep up or a vacuum leak expands, the system fails to compensate, triggering the code.

Will a fuel injector cleaner fix P2191?

A high-concentration fuel system cleaner dissolves minor deposits and sometimes resolves codes caused by lightly clogged injectors. However, it will not fix a severely clogged injector, a vacuum leak, a broken PCV valve, or a weak fuel pump. Use it as a first-step diagnostic, not a guaranteed cure.

Can bad gas cause a P2191 code?

Yes. Fuel contaminated with water, diesel, or high ethanol content (like E85 in a standard vehicle) alters the air-fuel ratio enough to trigger a lean code. If the problem started immediately after filling up, drain the tank and refill with high-quality gasoline.

Can a dirty air filter cause P2191?

No. A clogged air filter restricts air, causing the engine to run rich (too much fuel, not enough air). This triggers rich codes like P0172, not lean codes like P2191.

How much does it cost for a shop to diagnose a P2191 code?

Repair shops charge a diagnostic fee ranging from $125 to $185. This covers scanning codes, analyzing live data, and a visual inspection. Advanced tests like smoke testing or fuel pressure testing add $50 to $100 to the initial fee.

Key Takeaways

• P2191 indicates Bank 1 of your engine runs excessively lean (too much air, not enough fuel) specifically when accelerating or climbing hills.
• Do not replace the oxygen sensor first; diagnose the root cause by performing an intake smoke test and testing fuel pressure under load.
• A dirty Mass Air Flow (MAF) sensor or a cracked PCV hose causes over 40% of P2191 codes and can be fixed at home for under $50.
• Driving with an active P2191 code for more than 1-4 months overheats and destroys your catalytic converter, adding $1,200 to $2,800 in repair costs.
• If Long-Term Fuel Trims (LTFT) exceed +20% during acceleration, you have a confirmed fuel starvation or vacuum issue requiring immediate attention.