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you're sitting at a red light your
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foot's off the gas and suddenly your RPM
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starts bouncing like it's got a mind of
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its own you might think your car is
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haunted or worse breaking down but don't
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panic in this video we are going to
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discuss nine common reasons why your
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car's RPM goes up and down at idle and
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how to fix each issue before it becomes
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a major repair from dirty sensors to
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vacuum leaks we're diving into the real
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reasons your engine can't sit still
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stick until the end because the reason
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number eight is the most common culprit
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let's dive in reason one vacuum leak a
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vacuum leak introduces unmetered air
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into the intake manifold and disrupts
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the air fuel mixture making it harder
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for the ECU to maintain the stable idle
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common sources of vacuum leak include
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cracked vacuum hoses leaking intake
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manifold gaskets or disconnected PCV
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valves this lean condition causes the
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engine to surge or stumble at idle as it
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tries to compensate you might also hear
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a high-pitched hissing noise from under
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the hood or get a check engine light for
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lean mixture to fix it inspect all
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vacuum hoses for cracks or
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disconnections especially around the
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throttle body and intake a smoke test or
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carb cleaner spray around joints can
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help pinpoint leaks replace any damaged
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components and reset the ECU if needed
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to restore a smooth idle reason two
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dirty or faulty idle air control valve
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the idle air control valve plays a
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critical role in maintaining a steady
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idle by regulating the amount of air
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bypassing the throttle plate when the
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engine is idling the throttle plate is
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mostly closed so the IAC adjusts air
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flow to prevent stalling over time
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carbon deposits or dirt can clog this
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valve causing inconsistent air supply
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when this happens the engine struggles
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to maintain a consistent idle and the
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RPM may fluctuate unpredictably to fix
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this locate the IA valve and remove it
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now clean the valve thoroughly with
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throttle body cleaner if cleaning
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doesn't resolve the issue replacing the
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IA valve is the next step reason three
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faulty MAF sensor the MAF sensor
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measures the volume of air entering the
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engine and sends that information to the
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ECU for proper fuel metering if it
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becomes dirty or starts failing it can
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send incorrect air flow data causing the
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engine to run too rich or too lean both
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of which result in RPM fluctuations at
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idle you might also notice hesitation
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when accelerating poor fuel economy or
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stalling after starting to fix this
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issue remove the MAF sensor which is
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usually located just after the air
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filter box and clean it gently using MAF
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sensor cleaner let it dry completely
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before reinstalling if symptoms persist
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test the sensor with a multimeter or
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scan tool and replace it if it's giving
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incorrect readings after repair reset
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the ECU by disconnect the battery for a
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few minutes to recalibrate fuel trims
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bonus tip never use carb cleaner for MAF
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sensor reason four dirty or clogged
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throttle body the throttle body controls
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how much air enters the engine based on
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how much you press the accelerator over
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time carbon deposits and grime build up
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around the throttle plate restricting
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air flow and confusing the ECU this
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restricted air flow causes the engine to
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overcorrect by increasing or decreasing
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RPM rapidly leading to an unstable idle
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symptoms include surging stumbling or
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inconsistent idling to fix it remove the
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intake hose and spray throttle body
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cleaner around the throttle plate and
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bore use a clean cloth or brush to
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remove build-up carbon gently after
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cleaning many vehicles require a
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throttle position reset or an idle
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relearn process to restore proper idle
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control you can reset your throttle
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position sensor by using battery
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disconnection method or scan tool reason
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five bad spark plugs bad spark plugs are
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one of the silent killers of a smooth
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idle they're tiny cheap and often
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overlooked but when they go bad your
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engine's entire rhythm falls apart spark
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plugs are responsible for igniting the
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air fuel mixture inside each cylinder
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and when one misfires or fails to spark
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consistently the engine stumbles you'll
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notice the RPM jumping rough idling
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vibrations and sometimes even a flashing
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check engine light to fix it remove the
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spark plugs and inspect for wear oil
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fouling or improper gap replace them
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with the correct type and always check
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the gap before installation also don't
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forget to inspect your ignition coils or
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wires because sometimes the plug isn't
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the only problem reason six dirty fuel
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injectors fuel injectors are responsible
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for spraying fuel into the combustion
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chambers in a fine mist for proper
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combustion if they become clogged or
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dirty they fail to deliver consistent
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fuel leading to a lean or uneven burn
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this inconsistency causes the RPM to
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jump or drop at idle and in severe cases
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the engine may stutter or misfire to fix
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this use a highquality fuel injector
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cleaner additive in your gas tank over a
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few tanks of fuel for more serious
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buildup professional ultrasonic cleaning
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or oncar injector flushing may be
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required regularly using top tier gas
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and injector cleaner can help prevent
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this issue longterm if an injector is
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physically damaged it must be replaced
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reason seven ECU software glitch or idle
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relearn needed sometimes your car is
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just confused after replacing a battery
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throttle body or sensor your ECU may
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lose its learned idle settings that
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causes unpredictable RPMs until it
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recalibrates in modern cars the throttle
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and idle are electronically controlled
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so the ECU needs time or a procedure to
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relearn proper idle position you can
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help it out by doing a proper idle
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relearn start the car let it idle for 5
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to 10 minutes with no accessories on
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then turn on the AC for a few minutes
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always check your owner's manual or look
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up the correct steps for your car reason
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eight worn or loose drive belts a loose
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or worn serpentine belt can slip
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especially when accessories like the AC
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compressor or power steering pump engage
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this sudden change in engine load can
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cause brief RPM drops or surges as the
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engine compensates you might hear
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squeaking noises or notice inconsistent
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charging or steering effort to fix this
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inspect the serpentine belt for cracks
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glazing or looseness replace the belt if
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it's worn and also check the tensioner
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and pulleys a faulty tensioner might
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need replacement to maintain the correct
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belt tension keeping the belt system in
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good shape ensures stable engine
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operation and prevents idle surging
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reason nine faulty EGR valve the EGR
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valve reduces emissions by recirculating
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a small amount of exhaust gas into the
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intake but it should remain closed at
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idle if it becomes stuck open due to
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carbon buildup or a mechanical fault
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exhaust gases dilute the air fuel
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mixture causing rough idling and RPM
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fluctuation this often leads to stalling
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at stop lightss or engine hesitation
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under light throttle to fix this remove
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the EGR valve and inspect it for carbon
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buildup clean it with EGR valve cleaner
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and a brush or replace it if cleaning
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doesn't help after repair clear any
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related engine codes and perform an idle
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relearn if necessary that's all for this
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video so the next time your car's RPM
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starts bouncing at a stoplight don't
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panic listen it's trying to tell you
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something if this video helped you out
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give it a big thumbs up and smash that
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subscribe button for more real world car
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it in the comments below see you in the
