Won’t run when warmed up

I have a 08 Mustang GT, when its cold no issue .as it warms up it wont take gas, and idles real choppy in the 300-500 rpm range, I get no codes on anything, I have replaced the fuel pump and filter, cleaned the MAF, and T/B, replaced the throttle position sensor Fuel pressure sensor,throttle motor does work when its not running, I have tried the stock tune still no difference,plugs have been replaced 850 miles ago, Its not the gas filled other car at same place 1/2 after later and its fine

My car has 10210 miles.
My car has an automatic transmission.

Experienced mechanics share their insights in answering this question :
Hi there. It looks like you have inspected most of the common culprits of a choppy running engine. However, when the vehicle gets hot and has running issues, it’s commonly caused by the EGR valve or EGR valve temperature solenoid. As the engine gets warm, the exhaust gas recirculation valve can become stuck, leading to an lean engine condition, which typically lowers the RPM as you’ve indicated. Check this component, clean it, and see if that clears up your problems. If not, feel free to contact one of our professional mechanics to see if they can inspect the choppy engine issue and find the source of the problem.

How to Identify and Fix Common car Problems ?

Our sources include academic articles, blog posts, and personal essays from experienced mechanics :

Engine hunting and surging at idle is usually caused by a fuel delivery, air leak, or governor system problem. Cleaning/overhauling the carburettor, adjustment of the governor, and/or changing the air filer may be required.
The most common reasons a Ford Mustang has rough idle are a vacuum leak, an issue with the spark plugs, or a problem with the ignition coil. Search our network of RepairPal Certified shops near you to speak with a technician about your issue. Oops!
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).
Among the potential underlying causes are vacuum leaks, EGR system malfunctions, malfunctioning oxygen sensors, dirty fuel injectors, fuel pump malfunction, faulty spark plugs, a faulty mass airflow sensor, or a faulty throttle position sensor.
If your RPM starts fluctuating, there might be issues with the engine`s combustion process, a communication gap between the IAC and the ECU, or it can be a worn-out spark plug.
A rough idling engine can be caused by spark plugs or spark plug wires. Spark plugs use the electrical current received from ignition coils to ignite the air/fuel mixture within the combustion chamber. A plug that is damaged or installed incorrectly can result in fuel being burned at an inconsistent rate.
Engine Misfires

Perhaps the single most common cause of rough idle comes in the form of a misfiring engine. As you may know, any automotive engine contains multiple cylinders. Each of these cylinders contributes to powering your car by combusting a mixture of gasoline and air.

High RPM – Idle speed is measured in revolutions per minute (RPM). For most 2 liter and below sized engines the vehicles, the standard idle speed should be around 750 RPM (when the engine is warm). If your car`s RPM is above 900 with a warm engine while idling, it is likely using too much fuel.
The ideal RPM for any vehicle is 1500 RPM to 3000 RPM. In this range, you can save up on a lot of fuel by driving efficiently.
An RPM reading of 1 when parked may indicate a problem with the vehicle`s idle control system. It could be caused by a faulty sensor or a malfunctioning component within the engine. It is important to have the vehicle inspected by a qualified mechanic to diagnose and address the underlying issue.
High RPM – Idle speed is measured in revolutions per minute (RPM). For most 2 liter and below sized engines the vehicles, the standard idle speed should be around 750 RPM (when the engine is warm). If your car`s RPM is above 900 with a warm engine while idling, it is likely using too much fuel.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

Engine won’t fire without ether and runs bad until it warms up.
ANSWER : Hi there. There could be a lot of carbon build up inside the combustion chamber making the fuel not burn properly due to the valves and rings not sealing. First check the spark plugs and see if there is excessive build up on the terminal. If there is, clean off the plugs with a wire brush and put them back in. Start up the vehicle and put in sea foam into the intake through a vacuum hose. You will need to keep the engine running at about 2,500 rpm’s to allow the sea foam to work. The more black smoke that comes from the exhaust pipe will let you know of how much carbon is built up in the engine. Then, install new spark plugs and put a can of sea foam in the fuel tank and top off the fuel tank. This will stabilize the fuel and clean the fuel injectors. If you need further assistance with your engine running rough and having to start the engine with ether, then seek out a professional, such as one from Your Mechanic, to help you.

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After sitting without running for a long while, sometimes in-tank electric fuel pumps won’t start.
ANSWER : Check the power supply to the fuel pump, at the fuel pump terminals (as close as you can get) to be sure that the circuit actually functions. If there is power to the pump, but no operation, it is possible the fuel has oxidized, turned to varnish and other compounds, and basically glued the pump "shut". Also, it is not just a matter of air in the tank (oxidizing the fuel) but also moisture in the tank. Over so many years, the pump could be sitting in water simply due to accumulated water from condensation. If the tank has lots of water at the bottom, if it is a metal tank you might even need a new tank due to the possibility of internal corrosion. Although I suppose you could figure out a way to "unstick" a fuel pump that has sat in oxidizing fuel, and possibly water, for so many years, it is not worth it on account of safety and reliability considerations. If there is power and the pump doesn’t work, I would install a brand new pump and of course very carefully inspect the interior of the tank being mindful not to blow it up. Use a low power LED light…don’t use a 120 volt trouble light around fuel or, much worse, around fuel vapors. If you desire that the pump be replaced by a certified mechanic and the tank be inspected, simply request a fuel pump replacement. If you have additional concerns or questions, by all means please let us know.

Read Full Q/A … : Won’t run when warmed up

Jeep will crank but won’t turn over. Fuel pump running constantly and the ASD replay buzzing and alarm system won’t shut off.
ANSWER : Hi there, thanks for your question. I would recommend having the vehicle scanned to see what codes are coming up as this will direct you toward a potential solution.

Without knowing what codes may be coming up, some things to check or keep in mind might be the crank position sensor, cam position sensor, and coils. If you’d like some assistance, we can have one of our certified automotive technicians come to your home or office to inspect, diagnose, and make the necessary repairs to your Jeep.

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rebuilt motor won’t run well
ANSWER : Its possible for timing to be contributing to the cause, but 3 and 8 are not firing. Thats the bigger issue. Check for proper plug wire orientation, and check your plugs to see if they are wet, indicating that they are getting fuel. Also make sure that the distributor cap and rotor as no issues. You can use a timing light to see if the plugs are getting a spark by connecting the trigger lead to 3 and 8. The timing light should flash. if you still need help, a certified technician, like one from YourMechanic.com, will be able to determine the exact cause of your rough running engine.

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Why won’t my car stay running when it is cold
ANSWER : Hello, thank you for writing in. The vehicle may be suffering from several different issues. Depending on how cold the weather is, you may want to consider setting your car up for colder weather. This would include a thinner oil, new spark plugs, and proper anti-freeze. The battery issue you explained is a little confusing. If your new battery does not start the vehicle, but another battery does, you likely need to get a new or different battery. Look for one with a higher cold crank amps rating. All vehicles need more fuel and advanced spark timing when the engine is cold. Once the vehicle has started, you may want to have it scanned for codes. If you have any issues or codes from temperature sensors, this will also effect the starting and running conditions of the engine. These may need to be tested or replaced as well. Only further testing will tell.

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The car engine runs erratically when it is cold, then runs just fine after the car warms up after a while.
ANSWER : Try checking the coolant temperature sensor. When the engine is cold, the enrichment function relies heavily on the coolant temperature sensor to determine how much fuel to supply at lower temperatures. If this is not working properly, it may struggle to settle into a well running pattern. For example, if it is 30 degrees outside and the temperature sensor reads 100 degrees, this may send false information to the ECU causing it to send false information to the fuel injection system. A qualified professional from YourMechanic can inspect the rough running problem and verify the needed repairs.

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01 mustang v6 running rough at idle and drive. Please help. Replaced a bunch, still can’t figure out issue.
ANSWER : This may be a sign of a faulty MAP sensor as the vehicle responds adversely to a load put on the motor (i.e. putting it in gear, turning on AC or engaging the brakes). The Manifold Absolute Pressure (MAP) sensor senses engine load and generates a signal that is proportional to the amount of vacuum in the intake manifold. The engine computer then uses this information to adjust ignition timing and fuel enrichment. When the engine is working hard, intake vacuum drops as the throttle opens wide. The engine takes in more air, which requires more fuel to keep the air/fuel ratio in balance. When the computer reads a heavy load signal from the MAP sensor, it adjusts the fuel mixture to slightly more rich than normal so the engine can produce more power. The computer will then retard (back off) ignition timing slightly to prevent detonation that can damage the engine and decrease performance. This may also be caused by other closely related components such as a dirty or failing mass air-flow sensor, a faulty throttle position sensor or potentially a vacuum leak. I would recommend having an expert from YourMechanic come to your location to diagnose and inspect your vehicle.

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2008 Ford Mustang GT Stalls after warm up as if it ran out of gas and won’t restart until engine is cooled
ANSWER : The issue is the fuel pump relay on your fuel system. The fuel pump relay is getting hot and shutting off the fuel pump. Then when you shut off the engine and key to the ignition switch, the fuel pump relay cools off and then makes a good connection to the fuel pump. I recommend replacing the fuel pump relay.

If you need further assistance with your engine stalling after it starts sputtering when it is at operating temperature, then seek out a professional, such as one from Your Mechanic, to help you.

Read Full Q/A … : Won’t run when warmed up