A poorly functioning mass air flow sensor can mean poor engine performance and more, so it’s better to catch the bad mass air flow sensor symptoms early on.
The mass air flow sensor is a vital component of the electronic fuel injection system of a car. It monitors and controls the amount and temperature of air that enters the engine and communicates this with the Engine Control Unit (ECU) so it can send the correct amount of gas to the engine.
How Does the Sensor Work?
The mass air flow sensors measure the total volume of air that enters the engine by maintaining a constant temperature and a voltage signal that’s proportional to the air mass flow rate. The ECU should be able to deliver the right amount of fuel that complements and is proportional to the air flow.
Bad Mass Air Flow Sensor Symptoms
Below, I listed some of the most common symptoms that a car will show when the MAF sensor is bad.
1. Excessively rich at idling or lean when running
An engine running “rich” means that there’s a lot more fuel than air in each of the engine’s combustion cylinder. The air mass flow sensor overestimates the air flow and communicates the wrong value to the ECU.
Typical signs of running rich are dark black smoke coming out of the tailpipe and rough idling. These can also indicate lower fuel efficiency, meaning more trips to the gas station and a bigger hole in your pockets.
Running “lean,” on the other hand, is the opposite of running rich. There’s more air than there is gas. The air mass flow sensor underestimates the air flow, and again communicates the wrong value to the ECU.
Signs of running lean are hard engine seizures and hard starting. While running lean will get better fuel efficiency, it can damage the vehicle in the long run. A trip to the mechanic costs more than a trip to the gas station, so always be on the lookout for abnormal changes in the engine’s performance, even if the changes appear positive.
Engine hesitation and jerking forward or surging during acceleration means the ECU isn’t supplying the right amount of fuel when accelerating. This is more obvious when going uphill or sudden acceleration because the car needs more power.
A bad sensor will give the wrong air mass value and won’t allow the engine to quickly supply the power it needs. However, engine hesitation isn’t always obvious. The difference can be a matter of seconds, so it’s good to watch the engine closely when the car is demanding more power.
3. Gas smell from the exhaust pipe
It can also lead to the gas smell coming from the exhaust pipe. This is because the ECU isn't delivering the right amount of gas – and will sometimes deliver more than necessary. That excess will give off the gas smell.
5. Check if the engine light turns on
In most cases, if the ECU receives weird and out of range values from the air mass flow sensor, the engine light will turn on. Checking this light often is one of the best ways to make sure the engine is working well.
6. Engine halts
Engine halting is one of the major signs that the mass air flow sensor should be replaced. However, this is a symptom that can also mean damage to other parts of the engine. It’s best to have a mechanic look at it first to confirm the problem before choosing to replace the mass air flow sensor.
Problems with MAF sensors aren’t solitary cases, in fact, they’re common in cars like Toyota, Ford, Volkswagen, Silverado, and other brands. Hence, there is a lot of resources online on what to do when the system is bad.
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One of the most common reasons is that the MAF sensor is simply dirty. When an air filter isn’t properly installed, some debris can get sucked into the MAF sensor. A little clean-up will have the engine running smoothly again in no time.
How to Clean the MAF Sensor?
The first step is to locate the MAF sensor. It’s installed on the left side of the engine compartment, in the air intake tube or duct. Open the car’s airbox and carefully remove the sensor and disconnect it from its electrical connector. Most cars will require a Torx tool for Torx screws inside the airbox.
Before removing the air mass flow sensor, take a picture of what it looks like still attached so it’s easier to return it to its original place after cleaning. The next step is to spray the wire or plate 10-15 times with a mass air flow sensor cleaner.
Cleaners can be found at any auto parts store. Don’t use any other cleaner because this might damage the wires or plate, and will cost more money to fix!
Contrary to the usual cleaning, the sensor's plate or wires don't have to be scrubbed. Scrubbing may break the wire or damage the plate. After spraying, let the sensor air dry and then return it to the air duct.
Never reinstall the sensor to the engine while it’s still wet. This can attract even more dust and might allow clogging.
Lastly, be careful so as not to damage any wires when removing and returning the mass air flow sensor. Make sure all Torx screws are back in place, and everything is back to how it was before the sensor was removed.
As a general rule, sensors should be cleaned every 6 months or every time the air filter is changed or cleaned. Cleaning can cost only a few dollows while a replacement can cost the hundreds of dollows!
Can I Drive with a Bad MAF Sensor?
The short answer is yes, but not for a long time. It’s not advisable to keep running a vehicle with a bad MAF sensor because it may lead to even more severe engine problems.
If cleaning doesn’t do the trick, the only reason anyone should be driving a car with a completely broken MAF sensor is if they’re on the way to a mechanic!
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James is a certified auto technician specializing in commercial vehicles. With 30 years of experience under his belt, James has encountered almost every type of automotive issue there is! Besides his day job at the repair shop, he is also an amateur race car driver.