Note: Only use MAF sensor cleaner to clean a MAF sensor. Excessive oil may blow past the filter and gum up the MAF sensor. If you use an aftermarket air intake, make sure you don’t apply too much oil on the air filter. If not, test the MAF sensor to see if it’s gone bad and replace if necessary. A dirty sensor will often read incorrect air measurements, throwing off the air fuel ratio.Ĭleaning this sensor with a dedicated MAF sensor cleaner may solve the issue. Dirt and oil buildup that has blown past the engine air filter can easily foul the sensor. 3) Dirty or Faulty MAF SensorĪ mass air flow (MAF) sensor is responsible for measuring the amount of air entering the engine on most vehicles. These vehicles will raise the idle as if the throttle plate were open when they have a vacuum leak, and are unlikely to stall. This smoke will seep out from any holes in the intake system and tell you very quickly if air is able to enter the intake system where it should not be.Ī vehicle that uses a speed-density system for engine management will have a manifold absolute pressure (MAP) sensor instead of a MAF sensor. If you don’t have any immediately apparent leaks, you can perform a smoke test to find the exact source of the leak.ĭuring a smoke test, a mechanic pumps smoke into the intake system. You may be able to pop the hood and find something that’s noticeably out of place, such as a vacuum line that has torn or disconnected. If the leak is severe, the fuel injectors may not be able to keep up with all the extra unmetered air in the system for a proper burn in the combustion chamber. Normally a car will still run with minor vacuum leaks. This throws off the expected air fuel ratio and causes the vehicle to run lean (in other words, too much air for the amount of fuel that has been injected).Īn excessively lean air-fuel mixture could cause the vehicle to shake when starting, and then die shortly after. 2) Bad Vacuum LeakĪ vacuum leak is a hole in a vehicle’s air intake system behind the mass air flow (MAF) sensor that allows unmetered air into the engine. If the root cause is an electrical problem within the idle air control valve itself, you will likely have to replace the IAC. You can use a multimeter along with a factory manual’s wiring diagram to test the idle air control valve. Sometimes there is an electrical issue inside the idle air control valve that prevents the valve from operating properly. You can try cleaning the idle air control valve to see if it resolves the problem. This is a very temporary solution, but it could mean the difference from being stranded and getting safely to your destination. If you have a bad idle air control valve, you can often keep the engine running by giving it gas. When the idle air control valve malfunctions, you may experience a rough idle or the vehicle may stall entirely. It also manages the idle under changing engine loads, like when you kick on the air conditioning, turn on the headlights, or turn up the radio. 1) Bad Idle Air Control ValveĪn idle air control valve (IAC) regulates the air fuel mixture of a vehicle at idle. You don’t want to risk making a small problem worse if the issue ends up being a simple fix. This gives the starter a chance to rest, and may reduce the risk of flooding the engine. If you’ve attempted to start the vehicle a couple times without success, you should wait a few minutes before trying again. There are many reasons why your car would start and then stop immediately. 5) Bad Camshaft/Crankshaft Position SensorĬommon Reasons a Car Starts Then Shuts Off.Common Reasons a Car Starts Then Shuts Off.
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