Engine Misfires After Rain - Top Causes, Fixes & What to Do

Certified Professional Automotive Mechanic – Owner and Editor of VehicleRuns

Last Updated: September 29, 2026

Safety note: Troubleshooting guidance can help you narrow down likely causes, but it cannot replace an in-person inspection. If the vehicle feels unsafe, warning lights are flashing, you smell fuel, see smoke, notice overheating, or have problems with braking, steering, or control, stop driving when it is safe to do so and have the vehicle inspected.

If your engine starts running rough after rain, the weather is often more than a coincidence. A misfire that shows up in wet conditions usually means moisture is getting where it should not, or rain is exposing a weak ignition or electrical part that already had a problem.

The most common pattern is moisture affecting spark delivery. That can mean worn spark plugs, a weak ignition coil, cracked boots, or electrical connectors that no longer seal well. In some vehicles, water can also affect the air intake, MAF sensor, or other engine management components.

The key is to pay attention to when the misfire starts and what else changes with it. A rough idle right after startup points in a different direction than a misfire only under load, after driving through standing water, or only during humid weather. Some causes are relatively minor, while others can damage the catalytic converter or leave you stranded.

Start by matching the wet-weather pattern. The most useful split is whether the misfire starts at startup, only under load, after deep water, or with a check engine light flashing.

What you notice	Most likely cause	What to check first	Urgency
Rough idle right after a wet start	Moisture in ignition components	Inspect coils, plug boots, and plug wells for water	Can worsen
Misfire only when accelerating in wet weather	Weak coil under load	Scan misfire counts and inspect the affected coil	Can worsen
Problem started after driving through standing water	Water entering the air intake	Check air filter box and intake tract for moisture	Stop driving
Runs worse with a flashing check engine light	Active severe misfire	Stop driving and scan for stored misfire codes	Stop driving
Only happens in heavy rain or high humidity	Connector or ground fault	Inspect engine grounds and exposed connectors for corrosion	Diagnose soon

Best first move: If the engine still runs, begin with a code scan and a visual check of coils, plug wells, intake parts, and wet electrical connections before replacing parts.

Safety note: Do not keep driving with a flashing check engine light, severe shaking, or signs of water ingestion. A severe misfire can overheat the catalytic converter, and water in the intake can cause major engine damage.

Table of Contents

Most Common Causes of an Engine Misfiring After Rain

On most vehicles, a rain-related misfire comes down to moisture affecting spark, air metering, or electrical connections. The three causes below are the most common starting points, but a fuller list appears later in the article.

Moisture in Ignition Coils or Spark Plug Wells: Water around a coil boot or in a plug well can let spark leak to ground instead of firing the cylinder cleanly.
Worn Spark Plugs or Weak Ignition Coil: Rain and humidity often expose ignition parts that are already marginal, especially under acceleration or cold startup.
Wiring, Connector, or Engine Ground Fault: Wet conditions can worsen corrosion or poor electrical contact and cause intermittent misfires that seem weather-related.

What an Engine Misfire After Rain Usually Means

When an engine misfires after rain, the strongest clue is that moisture changes the problem. That usually points away from purely internal engine damage and toward ignition, sensor, intake, or wiring issues that become sensitive when wet.

If the misfire is worst right after startup and then improves as the engine warms, moisture around the coils, plug wires on older systems, or spark plug wells is very likely. Humidity lowers the resistance path needed for spark to leak, so a weak boot or cracked coil housing may fail only in wet conditions.

If the engine feels mostly normal at idle but stumbles under throttle, that often means the ignition system can barely keep up until cylinder pressure rises. A weak coil that passes a casual visual check can still misfire only during acceleration, hill climbing, or highway merging.

If the problem starts after driving through deep puddles or heavy spray, think beyond spark alone. Water can soak the air filter, disturb MAF readings, or reach a connector low in the engine bay. The more the symptom is tied to standing water rather than simple humidity, the more important it is to check the intake tract and lower wiring runs.

Possible Causes of an Engine Misfiring After Rain

Moisture in Ignition Coils or Spark Plug Wells

Modern coil-on-plug systems sit directly above the spark plugs, and water entering the plug wells or soaking the coil boots can create an easier path for spark to leak to ground. That causes a rough idle, stumble, and misfire that often shows up right after rain or washing the engine bay.

Symptoms to Watch For

Rough running right after a wet start
Misfire improves as the engine dries out
Visible moisture or oil in spark plug wells
One-cylinder misfire code such as P0301 through P0308

Moderate Severity

The car may still run, but continued misfiring can damage the catalytic converter and leave you with a no-start or severe drivability problem.

How to Confirm: Remove the coil from the misfiring cylinder and inspect the plug well for water, oil, corrosion, or carbon tracking.

Typical fix: Dry the plug wells, replace the affected coil boot or ignition coil, and replace spark plugs if they are worn or contaminated.

Worn Spark Plug or Weak Ignition Coil

Rain does not always create the fault by itself. Often it exposes an ignition part that was already near its limit. Higher humidity and wet conditions make it easier for a weak coil or overly worn spark plug to fail, especially under load.

Symptoms to Watch For

Misfire under acceleration more than at idle
Long overdue spark plug service
Intermittent check engine light in damp weather
Reduced fuel economy or hesitation

Moderate to High Severity

A mild misfire may seem manageable, but it often worsens quickly and can overheat the converter if you keep driving it hard.

How to Confirm: Check service history first, then scan for cylinder-specific misfire codes.

Typical fix: Replace worn spark plugs and the failing ignition coil, then clear codes and confirm the misfire is gone.

Wiring, Connector, or Engine Ground Fault

Rain can aggravate weak electrical connections by adding resistance or allowing current to track across corrosion. Engine grounds, coil connectors, injector connectors, and harness sections near the cowl or front of the engine bay are common trouble spots.

Symptoms to Watch For

Problem appears only in rain or high humidity
Intermittent misfire on more than one cylinder
Other electrical oddities at the same time
Green corrosion or loose connector locks

Moderate Severity

These faults can stay intermittent for a while, but they can also become a more frequent misfire or sudden stall if the connection worsens.

How to Confirm: Visually inspect connectors and grounds for corrosion, damaged seals, and loose terminals.

Typical fix: Repair or replace the damaged connector, terminal, harness section, or ground connection and protect it from future moisture intrusion.

Dirty or Faulty Mass Air Flow Sensor

A MAF sensor that is already dirty or drifting can misreport incoming air when humidity changes or when moisture affects the intake stream. That can cause the air-fuel mix to go off enough to trigger rough running or misfire-like hesitation.

Symptoms to Watch For

Stumble after rain without one clear cylinder code
Rough idle and hesitation together
Air intake parts recently disturbed or loosely fitted
Fuel trim readings unusually high or unstable

Moderate Severity

This usually will not cause immediate mechanical damage, but it can lead to repeated misfires, poor drivability, and converter stress if ignored.

How to Confirm: Use a scan tool to review fuel trims and MAF grams-per-second at idle and during light throttle.

How to Diagnose a Dirty or Faulty Mass Air Flow Sensor

Typical fix: Clean the MAF sensor with the correct cleaner or replace it, and repair any leaking or loose intake ducting.

Water Entering the Air Intake

Driving through standing water can soak the air filter or send water droplets into the intake tract. Even before true hydrolock, water contamination can disrupt airflow and combustion enough to cause misfiring, stumbling, or a no-start.

Symptoms to Watch For

Problem began right after a deep puddle
Wet or deformed air filter element
Severe stumble with little throttle response
Engine may crank unevenly after water exposure

High Severity

This is one of the more serious wet-weather causes because enough water can cause hydrolock and major internal engine damage.

How to Confirm: Open the air box and inspect the filter and intake tract for water, mud, or heavy moisture.

Typical fix: Dry and clean the intake system, replace the air filter, and repair or reposition damaged intake ducting or splash shielding.

Vacuum Leak or Unmetered Intake Air Leak

A cracked intake hose or leaking gasket can react differently in wet weather if moisture temporarily changes how the leak behaves or if movement and temperature shifts expose it. The result is a lean condition that can feel like a misfire, especially at idle.

Symptoms to Watch For

Idle is rougher than cruise
Hissing sound near the intake
Lean codes along with misfire codes
Misfire changes as the engine warms

Moderate Severity

A vacuum leak is usually not an immediate stop-driving issue, but it can cause stalling, poor drivability, and extra converter load over time.

How to Confirm: Look at short-term and long-term fuel trims for a lean pattern, especially at idle.

How to Find a Vacuum Leak in Your Car

Typical fix: Replace the cracked hose, PCV part, gasket, or leaking intake component and restore a sealed intake path.

How to Diagnose the Problem

Note exactly when the misfire happens: at startup, only in rain, after puddles, at idle, or under acceleration.
Scan for trouble codes before clearing anything. Cylinder-specific misfire codes and fuel-trim data can save a lot of guessing.
Open the hood and inspect for obvious moisture intrusion around ignition coils, plug wires on older vehicles, connectors, and the top of the engine.
Check spark plug wells for water, oil, or rust staining. On many engines, a leaking cowl seal or cover can drip directly into those wells.
Inspect the air box, air filter, and intake ducting for moisture, loose clamps, cracks, or signs of splash entry.
If one cylinder is flagged, swap that coil with another cylinder and see whether the misfire code follows the coil.
Review spark plug age and condition. Overdue plugs often turn a weather-sensitive misfire into a repeat problem.
Inspect engine grounds and electrical connectors for corrosion, broken seals, loose pins, or rubbed-through wiring.
If fuel trims are lean or unstable, smoke-test the intake system for vacuum leaks and inspect the MAF sensor and ducting.
If the engine was exposed to deep water or the misfire is severe with a flashing check engine light, stop driving and have the vehicle diagnosed before more damage occurs.

Can You Keep Driving If the Engine Misfires After Rain?

Important: The guidance below is general and cannot confirm that your specific vehicle is safe to drive. If a symptom affects braking, steering, handling, fuel, overheating, smoke, visibility, or vehicle control, treat it as potentially serious and have the vehicle inspected before continued driving when appropriate. For more context, see our Automotive Safety Disclaimer.

Whether you can keep driving depends on how severe the misfire is and what triggered it. A brief rough start in damp weather is different from a flashing check engine light after driving through standing water.

Okay to Keep Driving for Now

It may be okay to drive for now if the misfire was brief, the engine quickly smooths out, no warning light is flashing, and power feels normal. Even then, you should still diagnose it soon because wet-weather ignition problems usually come back.

Maybe Okay for a Very Short Distance

A short drive to a nearby shop may be reasonable if the engine is running rough but still controllable, the check engine light is steady rather than flashing, and there is no sign of water ingestion. Avoid hard acceleration, highway speeds, and long trips.

Not Safe to Keep Driving

Do not keep driving if the check engine light is flashing, the engine is shaking hard, power is dropping badly, the exhaust smells unusually hot, or the problem began after deep water exposure. Stop repeated restart attempts if you suspect water reached the intake or cylinders.

How to Fix It

The right fix depends on whether rain is exposing a weak ignition part, a moisture-sensitive electrical problem, or water entering the intake. The best repairs solve the root cause, not just the misfire code.

DIY-friendly Checks

Start with a code scan, inspect coils and plug wells for moisture, check the air box and filter for water, and look for loose intake ducting or obviously corroded connectors. Replacing overdue spark plugs is also a common first-step maintenance repair.

Common Shop Fixes

Many cases are resolved by replacing one or more ignition coils, installing new spark plugs, cleaning or replacing the MAF sensor, or repairing a bad connector or engine ground. Shops can also smoke-test the intake for leaks that are hard to see.

Higher-skill Repairs

More involved cases may need wiring repair, harness pin replacement, advanced live-data diagnosis, or inspection after water ingestion. If the engine was exposed to deep water, a shop may need to confirm there is no internal engine damage before normal use.

Related Repair Guides

Typical Repair Costs

Repair cost depends on the vehicle, labor rates, and the exact reason the engine misfires in wet weather. The ranges below are typical U.S. parts-and-labor estimates, not model-specific quotes.

Spark Plug Replacement

Typical cost: $120 to $350

This is common when worn plugs are making a damp-weather misfire easier to trigger, with cost varying by plug count and engine access.

Ignition Coil Replacement

Typical cost: $150 to $450 per coil

Cost depends on coil price and access, and some engines need only one coil while others are best serviced in pairs or sets.

Connector or Ground Repair

Typical cost: $100 to $350

This usually applies when corrosion, loose terminals, or a damaged ground point is causing an intermittent wet-weather misfire.

MAF Sensor Cleaning or Replacement

Typical cost: $80 to $350

Cleaning is cheap if the sensor is just dirty, while full replacement costs more when the sensor itself has failed.

Vacuum Leak Repair

Typical cost: $100 to $500

A simple hose is inexpensive, but intake gasket or buried leak repairs can push the total higher.

Water-damaged Intake Service

Typical cost: $100 to $600+

Drying the intake and replacing the filter is modest, but costs rise fast if standing water exposure leads to deeper inspection or engine damage concerns.

What Affects Cost?

How many cylinders or coils are affected
Engine layout and access to plugs or coils
OEM versus aftermarket ignition and sensor parts
Whether diagnosis finds a simple wet connector or a wiring repair
Any catalytic converter or water-ingestion damage caused by continued driving

Cost Takeaway

If the misfire is limited to overdue plugs, one coil, or a wet connector, the repair is often on the lower end. Costs rise when multiple coils are weak, intake leaks require disassembly, or water exposure means the intake and engine need deeper inspection. A flashing check engine light or deep-water event usually means you should think in terms of diagnosis first, not parts guessing.

Symptoms That Can Look Similar

Parts and Tools

FAQ

Why Does My Car Only Misfire when It Rains?

That usually means moisture is affecting a weak ignition part, electrical connector, ground, or the intake system. Rain often exposes a fault that is already there rather than creating a brand-new problem.

Can Rain Ruin Ignition Coils or Spark Plugs?

Rain itself usually does not ruin them instantly, but moisture can get past worn boots, cracked housings, or poor seals and make a marginal coil or plug start misfiring. If the problem keeps returning in wet weather, replacement is often needed.

Is It Safe to Drive with a Misfire After Rain?

Only if the misfire is mild, brief, and there is no flashing check engine light. If the engine is shaking hard, losing power, or the problem started after standing water, you should stop driving and have it checked.

Can a Wet Air Filter Cause a Misfire?

Yes. A soaked air filter or water in the intake can disrupt airflow enough to cause stumbling or misfire, and severe water entry can become a much bigger engine risk.

Will the Misfire Go Away Once the Engine Dries Out?

Sometimes it will improve temporarily, but that does not mean the problem is fixed. Moisture-sensitive misfires usually come back until the weak coil, worn plug, bad connector, or intake issue is repaired.

Final Thoughts

An engine misfire after rain is usually narrowed down fastest by treating the weather as a clue, not a coincidence. Start with the pattern: wet startup, humid acceleration, or standing-water exposure. That tells you whether to focus first on ignition parts, electrical connections, or the intake system.

Most cases come back to moisture around coils or plugs, worn ignition parts, or wet-sensitive wiring. A quick scan, a careful visual inspection, and attention to where and when the misfire happens will usually point you in the right direction before you start replacing parts.