Cadillac XT5 Rough Idle Causes + Diagnosis | Drivetrain Resource

Drivetrain Resource

If you own a Cadillac XT5 and it’s idling rough, you may be feeling frustrated. In this article, we’ll look at some of the most common causes of a rough idle in the XT5 and how to fix the problem. 

Cadillac XT5 Idling Rough

The most common cause of a rough idle is misfiring.

What an Engine Needs to Idle Smoothly

Your XT5’s engine needs air, fuel, and spark to achieve optimum ignition.  When one or more of these variables is off, it can lead to a rough idling condition.

  • Fuel– The ideal air-to-fuel ratio is 14.7 parts air to one part fuel.
  • Air– The air entering your vehicle’s engine must be metered by the MAF or MAP sensor.
  • Spark– The spark needs to happen at the right time, with the right amount of heat.  If it doesn’t, your XT5’s engine won’t idle smoothly.

Fuel and air are somewhat interlinked since they must enter the combustion chamber in the right combination for your vehicle’s engine to run smoothly.

Rough Idle Causes: Cadillac XT5

Here are the most common reasons your vehicle

Ignition System

Rough Idle Causes Cadillac XT5

Here are the main components of the ignition system, as well as what would cause them to make your XT5 idle roughly.

  • Spark Plugs–  One of the absolute most common causes (if not the most common reason that your XT5 may be misfiring) is the spark plugs.  Although most modern vehicles use iridium spark plugs, they must be changed at the manufacturer’s recommended interval.  This page has a great chart to compare your spark plug condition to new plugs.
  • Ignition Coil Packs–  Nearly all model years and engines use coil packs.  These packs are fired by the PCM (powertrain control module) at precisely the right time to provide the optimal ignition timing.  If a coil pack goes bad, it’ll cause a misfire and rough idle condition.  Your XT5 will run 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 XT5 happens to have plug wires, they can go bad and cause a rough idle.  Here’s a great video on how to diagnose bad plug wires with a multimeter.  You can also open your hood with the engine running at night and see if you see any spark jumping off of them.

Air Filter

If you have reason to suspect that your XT5’s air filter has not been changed in a long time, or if you have recently been driving in tough conditions, it may be worth looking at it.

It could be so clogged that there is not enough air getting through for quality 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, often the problem, cheap, and easy to replace.

Oxygen Sensors

The oxygen sensors that are equipped in your Cadillac XT5 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 XT5 run too lean (or rich).  A super lean running engine will often idle rough.

Vacuum Leak

A vacuum leak allows air to enter the combustion chamber unmetered, which increases the air in the air/fuel mixture.

A visual inspection will The most common place to find an intake leak is around the intake manifold.  Look for brittle or broken vacuum hoses. 

Dirty Fuel Injectors

Fuel injectors need a lot of fuel pressure to produce a fine mist.

Fuel injectors are responsible for delivering fuel to the engine, and a dirty fuel injector can cause problems such as a rough idle.  Dirt, grime, and other contaminants can build up in the fuel system over time, leading to clogged or blocked fuel injectors. 

Common sources of dirt in the fuel system include old fuel, dust, and dirt. A thorough cleaning of the fuel injectors will usually restore proper fuel pressure and get your XT5 idling smoothly again.   

For more, check out Cadillac XT5 bad fuel injector symptoms.

Mechanical Issues

Your Cadillac XT5’s engine needs to be mechanically sound.  Major mechanical problems can result in a rough idle.

  • Engine timing
  • Low compression in one or more cylinders
  • Exhaust leak
  • Worn piston rings
  • Metal shavings in oil

Cadillac XT5 Rough Idle Diagnosis

Start With the Check Engine Light

If your XT5’s check engine light is on, there will be codes stored that can help you determine what part of your vehicle’s engine is having problems.  

You can either go to the local parts store and ask them to scan the vehicle for you, or you can do this yourself.  Most of them will scan it for free.

Alternatively, code scanners are pretty affordable.  Having one of your own can save you a ton of time.

Once you get the trouble codes, you can use that information to determine whether it’s an O2 sensor, spark plugs, coil packs, etc, that may be causing the trouble.  Here are the most common problems that would cause a Cadillac XT5 to idle rough.

Where to Start if There’s No Code

If there’s no trouble code, it can be difficult to determine why your XT5 is running rough.

  • Check for vacuum leaks.
  • Verify that the throttle body and MAF are clean.
  • Inspect the spark plugs.
  • Test the fuel pressure.
  • Test the compression.


If your Cadillac XT5 is idling rough, look for any OBD II codes if the check engine light is on. If it is not, start with pulling the plugs and visual inspection of the air filter and vacuum hoses.

Start by taking a look at the codes, if the check engine light is on, and work from there.

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