Car revs at stop sign, no check engine light
So I have to get my exhaust completely replaced, that I already know, but now I'm driving and my car accelerates slowly but it revs, and then if I'm at a stop sogn or a light and go to hit the gas a little the RPM goes up to about 2/3. Or if I'm sitting there it will idle sometimes. I called my mechanic and he didn't seem to eager to have me come in.
My car has 130000miles.
Experienced mechanics share their insights in answering this question :
This may be a result of a faulty oxygen sensor reading as a result of your exhaust system (presumably your catalytic converter) not operating effectively. As you may know the oxygen sensors which are part of your emissions system read exhaust gases to determine whether or not the appropriate amount of oxygen is present in the exhaust. Based upon this reading, this information is relayed to the car’s ECU which then makes a determination as to whether or not to add more or less fuel to the engine. When too much or too little oxygen is present, this will cause check engine light to come on. Too much oxygen may be present in the exhaust gas due to things like an exhaust leak, a vacuum leak, a faulty mass air flow sensor (causing a lean fuel condition) or faulty fuel injectors. Too little oxygen may be present in the exhaust gas may be caused by things like a clogged air filter, a failing mass air flow sensor (causing too much fuel to be introduced to the motor), bad fuel injectors or a clogged catalytic converter. When the O2 sensor is not working properly, this will cause false readings to be relayed to the computer causing inaccurate adjustments to be made to the intake and fuel system in your engine. You may also notice a very strong smell of fuel. I would suggest having an expert from Your Mechanic come to your home to diagnose your emissions system.
How to Identify and Fix Common car Problems ?
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A rough idle may be caused by many different things such as low fuel pressure, low voltage to the fuel injectors, dirty fuel injectors, a vacuum leak, a faulty Oxygen sensor or a dirty or failing idle air control valve.
There`s only one thing that will cause a converter to glow red. That is too much air and fuel. The most common reason is the engine is misfiring. If your engine is shaking, and does not have power, it is misfiring.
Code P0420 indicates that the catalytic converter is not functioning efficiently, therefore increasing the output of harmful pollutants by the vehicle.
In order to understand this, it is important to know that a catalytic converter operates at a thousand degrees or more. If your engine develops a miss (which means one or more cylinders are not firing), it will result in a rough idle.
While some cases are less severe than others, a rough idle is usually identifiable by a shaking and bouncing sensation in the vehicle. You may also notice odd sounds, as well as inconsistent RPM counts. Normally, a vehicle should have a smooth and consistent RPM rate of around 1,000.
Causes of a rough idle. Many different problems could result in a rough idle for your car or truck, including: dirty fuel injectors, clogged air filters, bad spark plugs, and a variety of exhaust system issues.
Yes, a bad catalytic converter can cause a rough idle. This is because less exhaust will be able to escape, in turn reducing the amount of oxygen that can enter and combust in the engine. It`s best practice to replace the catalytic converter sooner than later.
A P0420 code is set when the upstream sensor and the downstream oxygen sensor sense the catalytic converter is not doing its job. Basically, the amount of oxygen going into the converter is not being burned, and it detects it through the downstream sensor.
Most catalytic converter failures fall under one of three categories: Overheated, melted or broken converters.
Normal operating temperatures of a converter are 500-800°F, and up to 1200°F when the vehicle is under heavy load. To melt the catalytic converter`s substrate, the temperature inside the converter would have to exceed 2000°F.
An idle air control valve, also called an idle air sensor control motor, is an electrically operated valve that controls the amount of air that bypasses the throttle plate in cars with a fuel injection system [source: Autozone]. This causes the idling speed of the engine to change as needed.
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.
How to fix it? Cleaning or replacing the fuel filter and adding a fuel injector cleaning treatment to the fuel tank should take care of clogged fuel injectors. If the rough idle persists, it`s time to take your car to an auto repair shop.
A PCV valve that`s stuck open will allow too much air to enter the intake manifold, leading to a leaner idling fuel-air mixture. Stuck closed leads to a build up of pressure in the crank case which creates a variety of oil leaks! And this in turn can lead to a range of issues, including a rough idle.
In short, yes; it`s possible to diagnose a problem with a vehicle even if the check engine light does not illuminate.
In short, yes; it`s possible to diagnose a problem with a vehicle even if the check engine light does not illuminate.
While it may seem like a small problem on its own, rough idling is a sign that some part of your engine isn`t working properly. Over time, rough idling can result in poor gas mileage, starting issues and major engine problems.
While it may seem like a small problem on its own, rough idling is a sign that some part of your engine isn`t working properly. Over time, rough idling can result in poor gas mileage, starting issues and major engine problems.
Potential causes of a vehicle shaking at idle include a loose gas cap, loose battery cables, a worn throttle sensor, a damaged engine mount, or bad spark plugs. Perform a general inspection of your engine bay to look for damage. If you can`t repair the problem yourself, take the vehicle to a mechanic.
In general, a misfire is the only reason the light will flash on and off. Keep in mind that the light may stop if the misfire stops at any point. You should also be mindful that if you see any sign of a misfire without the light flashing, the engine could still be misfiring.
While it may seem like a small problem on its own, rough idling is a sign that some part of your engine isn`t working properly. Over time, rough idling can result in poor gas mileage, starting issues and major engine problems.
In general, a misfire is the only reason the light will flash on and off. Keep in mind that the light may stop if the misfire stops at any point. You should also be mindful that if you see any sign of a misfire without the light flashing, the engine could still be misfiring.
While it may seem like a small problem on its own, rough idling is a sign that some part of your engine isn`t working properly. Over time, rough idling can result in poor gas mileage, starting issues and major engine problems.
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