Idles high randomly
Truck revs up to 3000 rpms stays there for a good while, already replaced tps and idle air control removed and cleaned throttle body
My car has 150000 miles.
Experienced mechanics share their insights in answering this question :
The only thing that can cause the engine to run this high of an idle is a vacuum leak and a misadjusted throttle body.
Try having the engine checked to see where the vacuum leak is. The most common area for a leak is at the throttle body shaft and intake gasket. Also, check the PCV valve hose for any leaks that will introduce extra air into the intake without passing through the idle air valve.
If you need assistance with this, have a qualified technician find the source of the leak and accurately repair your high engine idle.
How to Identify and Fix Common car Problems ?
Our sources include academic articles, blog posts, and personal essays from experienced mechanics :
Malfunctioning Throttle: A malfunctioning throttle system can cause both a high or low idle as well as an engine stall. A dirty air intake or cracked air intake tube is often the culprit. Computer Malfunction: If the powertrain control module is malfunctioning, idle speed may be affected.
The engine`s oxygen sensor will detect the extra oxygen entering the engine via the vacuum leak which will alert the engine`s computer that the exhaust is running lean, which will prompt the computer to pump in additional fuel, resulting in an abnormally high idle.
If the PCM offers no hints, the best place to begin looking for problems is with the Idle Air Control Valve/Bypass Air Control (IACV/BAC). You can try cleaning it and see if that improves your idle speed. A throttle body cleaning is likely to cure the high idle speed as well.
Often this is a result of dirt buildup in the air intake. Other times it can be a problem with a cracked intake tube. If the IAC motor`s vacuum port is leaking, this can be another cause of high engine idling. The leak could be sourced at the seal, or more often, in one of the attached hoses.
Malfunctioning Throttle: A malfunctioning throttle system can cause both a high or low idle as well as an engine stall. A dirty air intake or cracked air intake tube is often the culprit. Computer Malfunction: If the powertrain control module is malfunctioning, idle speed may be affected.
High idle engine switches—also called high idle controllers, or high idle kits—are used in a variety of industries in which end-users require high power from a vehicle when it`s not in motion. Common applications include armored and security vehicles, work trucks, buses and motor coaches.
Common faults caused by a dirty MAF sensor include: rough running at idle, increased fuel consumption, low power, poor throttle response, poor starting and black smoke (diesels).
Problem Description
Bad throttle position sensors can cause high idle without causing the Check Engine Light to illuminate.
The idle speed should feel consistent without skipping or slipping. In most of today`s cars, an idle speed of 600 to 1000 RPMs is average. If your car is idling rough, though, it won`t feel smooth. The RPMs will jump up and down, for example, or they`ll fall below 600 RPM (or whatever is typical for your vehicle).
Yes , if the engine base timing is increased, idle speed will increase. .
A faulty positive crankcase ventilation (PCV) valve may also cause an unusually high idle speed. This is similar to a vacuum leak, since the PCV valve routes crankcase gases into the intake manifold where they combine with the air fuel mixture.
Other possible causes of a high idle include vacuum leaks, EGR system malfunctions, malfunctioning oxygen sensors, dirty fuel injectors, fuel pump malfunction, faulty spark plugs, a faulty mass airflow sensor, a malfunctioning throttle and, rarely, a PCM/ECM malfunction.
High idle reduces soot in the exhaust which results from incomplete combustion at low engine revs. This is important because when diesel engines are operating at low RPMs, more soot is generated. That can fill up the diesel particulate filter (DPF) which has been installed on diesel engines since 2008.
An engine `runs away` when it revs uncontrollably and often extremely quickly. This could be caused by a few things but in all cases unregulated fuel and air are entering the combustion chamber, effectively causing the engine to go crazy without you telling it to. To stop it is simple; cut the fuel/air/ignition supply.
Idling will increase maintenance cost and shorten the life of the engine. Myth: Diesel engine idling does not waste much fuel. Fact: Fuel is one of the largest operating expenses in our industry. Idling adversely impacts us by increasing fuel and maintenance expenses.
Relevant Questions and Answers :
the most relevant questions and answers related to your specific issue
High idling, jumping while idling, idle air control valve code
ANSWER : Hi there. This can be caused by the issues that you mentioned or a number of other things. You need to make sure all of the connectors are making good contact. I would then need to know what codes are in the computer to know if this is a circuit issue or not. Most of the time, it is not the circuit but instead a vacuum leak.
If there is a vacuum leak, then the vehicle will act like this and the computer cannot control the idle. Most of the time it is a bad hose or an EGR valve that is stuck open. That is the most common cause for this. I typically remove the EGR to check it to feel the diaphragm on the bottom of it to see if it is moving correctly. If you need to have this repaired, consider YourMechanic, as a certified mechanic can come to your home or office to diagnose and repair your car’s idling issue.
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High Idle, stalls when a/c or defrost is turned on and dies completely after some rough idling. If turned back off car is fine.
ANSWER : Hi there. The fact you able to get the idle speed to drop by tapping the gas pedal, lead me to believe the high idle is due to a sticking accelerator cable. Another possibility could be, a faulty throttle body not allowing the throttle to return to the closed position. Proper diagnoses should be performed to avoid unnecessary repairs. I recommend having your vehicles high idle be diagnosed and repaired by a certified technician, such as one from YourMechanic.
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Why does my van always stay at a high idle 2000 Chevrolet Express
ANSWER : Hello. There are a lot of reasons that would cause a high idle, but most of the time it is caused by a vacuum leak. When there is an excessive amount of air entering the engine the computer will compensate with more fuel causing a higher idle. Most of the time the issue is in the intake manifold gasket. I would typically start by checking the engine sensor readings with a scan tool and then check for vacuum leaks with either propane enrichment or by performing a smoke test. If you need to have this idle issue repaired, consider YourMechanic, as a certified mechanic can come to you to [diagnose this high idle problem] https://www.yourmechanic.com/services/engine-idle-speed-is-high-inspection
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Truck idling high and shifting at high RPM when let off throttle
ANSWER : Hi There,
What you are describing sounds like possibly a bad speed sensor or potentially a faulty transmission control module, which also controls the speed sensors. The transmission control module has various sensors such as vehicle speed sensors, wheel speed sensors, throttle position sensors, turbine speed sensor, and transmission fluid temperature sensors that all direct information to it in order for it to perform it’s function. Other functions controlled by the TCM are components such as a kick down switch, traction control system, and cruise control module. Any of these may also affect the way the transmission control module performs and controls the transmission and the shifting of your vehicle. A faulty transmission control module may cause also cause a delay in acceleration or erratic shifting of gears. Lastly, this may also be a result of low transmission fluid. I would suggest having a professional from Your Mechanic come to your location to properly diagnose your transmission problem.
What you are describing sounds like possibly a bad speed sensor or potentially a faulty transmission control module, which also controls the speed sensors. The transmission control module has various sensors such as vehicle speed sensors, wheel speed sensors, throttle position sensors, turbine speed sensor, and transmission fluid temperature sensors that all direct information to it in order for it to perform it’s function. Other functions controlled by the TCM are components such as a kick down switch, traction control system, and cruise control module. Any of these may also affect the way the transmission control module performs and controls the transmission and the shifting of your vehicle. A faulty transmission control module may cause also cause a delay in acceleration or erratic shifting of gears. Lastly, this may also be a result of low transmission fluid. I would suggest having a professional from Your Mechanic come to your location to properly diagnose your transmission problem.
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Idle too high. 1994 Chrysler New Yorker
ANSWER : Hey there, thanks for writing in about your 1994 Chrysler New Yorker. Start your engine and let it idle in park for at least 5 minutes. Listen and check the engine for any vacuum leaks or inlet air tube leaks. Any vacuum leaks will result in a higher than normal idle. You may need to use a rubber hose to your ear to isolate any vacuum leak. You will hear a sucking sound when you find it. For help having this resolved, a professional from YourMechanic can come to your car’s location to inspect the high idle and let you know what repairs are needed.
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After replacing the power steering pump there was a low idle, idle screw is all out, running rich, and idle speed doesn’t change.
ANSWER : Hi there. The engine has a vacuum leak and is causing the engine to stumble down on the idle. Check all of the vacuum hoses and the brake booster for any leaks. The engine is rich for it’s not burning all of the fuel properly and may also have bad spark plugs. If you need further assistance with engine not adjusting the idle, then seek out a professional, such as one from Your Mechanic, to help you.
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Throttle body changed 3 days ago. Idle relearn performed and still high idle and revving while in park.
ANSWER : Hi there. Check the engine for a vacuum leak. Check all vacuum lines, hoses, and the intake for any leaks. Also check the brake booster for any leaks. A vacuum leak will increase the engine’s idle speed while the engine is not loaded. If you need further assistance with your engine revving in neutral and park, then seek out a professional, such as one from Your Mechanic, to help you.
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Wont idle unless idle is turned very high. New filter,rebuilt carb,new lines.
ANSWER : I would definitely agree that your idle issue (especially on an older engine) is most likely a vacuum pump problem. However, it could be as simple as a stuck float bowl in the carb or idle adjustment screw that is faulty. I would recommend first replace the vacuum pump and check all vacuum lines. You might want to also verify the idle adjustment is accurate
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