It can be a very jarring feeling when your Ford Mustang shakes when at idle. It can feel like the whole thing is going to vibrate to death with you in it. If your Mustang has this problem, there are many issues that can cause it. We’ve lined out some of the most common causes below.
Ford Mustang Shaking When Idling Diagnosis
There are a lot of reasons why your Mustang may shake when idle. Before you go trying to figure out which one is causing your Mustang to feel like it’s on spin cycle, make sure that the check engine light isn’t on.
If it is, get the trouble codes. That’s a great place to start. You can get a code scanner really cheap. Alternatively, most auto parts stores also provide the scan free of charge. With these diagnostic codes you’ll know which sensor is reporting a problem and by addressing it, hopefully it’ll fix your shake at idle speed.
1. Ignition System
The ignition system is responsible for burning the air fuel mixture that enters the combustion chamber. If a good spark is not achieved, your Mustang will shake as it misfires and tries to stay running.
Here are the main components of the ignition system, as well as what would cause them to make your Mustang shake when idling.
- Spark Plugs– One of the absolute most common causes (if not the most common reason that your Mustang may be shaking) is the spark plugs. Although most modern vehicles use iridium spark plugs, they still need to be changed at the manufacturers recommended interval. This page has a great chart for you to compare your spark plug condition to new plugs. Here’s more on bad spark plugs.
- Ignition Coil Packs– Nearly all model years and engines use coil packs. These packs are fired by the engines computer at exactly the right time to provide the optimal ignition timing. If a coil pack goes bad, it’ll cause a misfire and rough idle condition. Really, your Mustang will be running rougher at any RPM, but a misfire will be most pronounced at idle.
- Spark Plug Wires– While not every model and engine combination of vehicles today comes with spark plug wires (a lot are now coil on plug), if your Mustang happens to have them, they can go bad and cause a rough idle. Here’s a great video on how to diagnose bad plug wires with a multimeter.
2. Vacuum Leak
Your Mustang’s engine creates vacuum when running. This vacuum is carefully controlled. If the vacuum system gets a leak, it will cause a shake when idle.
A vacuum leak can be caused by a bad vacuum hose, intake manifold gasket, and other vacuum powered accessories. Diagnosing a vacuum leak can be tricky. Here’s a good YouTube video on how to do just that.
3. Motor Mount
Your Mustang’s motor mounts connect it to the chassis. If they wear out, it can cause it to shake when idle. You should also feel the shaking more in gear than when you are in park. It would also feel a little wobbly as the gears are shifted.
An engine misfire is the most common cause of a shaking idle, and as the engine stumbles and misfires, that should be seen in the tachometer as a drop in RPM. If the tachometer is rock steady, and the shaking seems worse in gear than out of gear, that’s a pretty good indication of a bad motor mount.
4. Timing Belt/Chain
If the timing belt or chain has jumped a tooth, the camshaft(s) and crank will no longer be lined up properly. If this happens it can cause the idle characteristics to change. Here’s more a whole article on timing chain jumped symptoms, if you have reason to believe this could be your problem.
5. Air Filter
If you have reason to suspect that your Mustang’s air filter has not been changed in a very long time, or if you have recently been driving in tough conditions, it may be worth taking a look at it.
It could be so clogged that there is not enough air getting through for proper idle conditions. In fact, if your check engine light isn’t on at all, checking out the air filter would be a great place to start. It’s readily accessible, sometimes the problem, and super cheap and easy to replace.
6. O2 Sensors
The oxygen sensors that are equipped in your Ford Mustang are responsible for monitoring the exhaust to help the ECU determine the correct air/fuel mixture.
Of all the sensors equipped in your vehicle, the O2 sensors may have it the hardest. They deal with super hot exhaust that can cover them in deposits that can leave them ineffective. The heat of the exhaust can also bake the wiring going to/from them over time.
If an oxygen sensor goes bad, it can make your Mustang run too lean (or rich). A super lean running engine will often shake when idling. The mixture would be wrong at all RPM, but as the engine speed increases the shaking decreases.
7. Fuel Injectors
Your Ford Mustang’s fuel injection system atomizes the fuel into a fine mist. If a fuel injector is not operating properly, it will either let too much or too little fuel into the combustion chamber relative to the amount of air. There are many reasons why a fuel injector may go bad, as well as different symptoms relative to how they went bad. For more, check out Ford Mustang bad fuel injector symptoms.
Diagnosing why your Ford Mustang is shaking when idling can be challenging, particularly if you don’t have any engine trouble codes to go off of. If there is anything that you would like to add, please leave a comment below. Good luck!