Why Does My Ford F150 Idle Up and Down?

Why Does My Ford F150 Idle Up and Down

Engine idling is a necessary function when your F150 stands still so that the engine can stay at a constant temperature. Despite the Ford F150 engine’s excellent design, there are some associated problems. 

For example, some drivers have reported how their Ford F150 idles up and down… here’s why in short, followed by a more in-depth analysis to help you get more from your truck.

Why does my Ford F150 idle up and down? A Ford F150 will idle up and down due to different engine problems including a clogged air filter, faulty ignition timing, vacuum leaks, corrosion, and others listed below.

F150 idles up and down

Engine idling-related problems, engine overheating, and driving up and down can happen in F150s. When the machine idles up and down, the engine is firing off at different speeds – this prevents it from staying at a constant temperature.

Prolonged engine idling increases fuel consumption, low exhaust gas air volume, low power, lean air-fuel mixture, and rough idle.

To help you diagnose and fix your Ford F150’s idle problems, I’ve compiled a list of common reasons why your F150 engine will be idling up and down at random times or after being shut off. 

F150 idles up and down
When you’re stuck in traffic is the time you will notice your Ford F150 idles up and down. (Image licensed via Storyblocks.com)

You can also see some of the possible solutions I’ve found that you can use to fix the problem. You should be able to diagnose and repair your idle up and down issue in no time.

Why does my F150 engine idle up and down?

When the Ford F150 engine idles, the oil pump circulates oil through the various components of the engine to keep them lubricated. It keeps your engine from wearing out at a faster rate and other problems from happening. 

If you notice that your Ford F150 idling is up and down, then something could be wrong with the engine. Rough idling results from engine-related malfunction like overheating and poor fuel flow into the combustion chamber-ignition system faults like leakages and corrosion within this system. 

The spark plug might not be firing on time and causing a misfire – possibly even causing an acceleration jerk as well. The pump may also fail to generate enough fuel pressure required for continuous ignition. Here’s those possible idling problems in more detail.

1. Clogged air filter

The air filter is one of the critical components of your vehicle’s fuel injection system.

When an air filter is dirty, your truck will not be able to burn up all the fuel that it is throwing at the engine; thus, your F150 can idle up and down, will become very unsteady and may even stall at times.

The air filter is located right underneath your hood, right behind your grill. Fix it by taking the air filter out and cleaning (or replacing it), depending on its current condition.

Amazon sell air filters that are compatible with Fords, click here.

2. Ignition timing is off

Ignition time is the time interval between spark and mixture. Your F150 may be idling up and down due to the ignition timing is off, or because of a bad distributor. To fix this, you will need to shorten it down.

The easiest way to do this is to use an adjustable timing tool (view on Amazon) that will allow you to adjust the timing properly until your idle smooths out. Another option for shortening ignition time is installing a new electronic ignition module and changing the module settings appropriately.

With the F150 engine idling up and down, this can cause a problem with your gas mileage because it will not be able to burn up all the fuel injected into the engine.

3. Vacuum Leak

Ignition only occurs when there is enough air and fuel to support it. sometimes fuel may fail to leach the combustion chamber. we call this disorder vacuum leak.

A vacuum leak is when the engine cannot pull in enough air because of a leak. This leak will cause the engine to idle up and down. We can either fix the leak or install a performance intake system to improve the airflow rate.

4. Corroded fuel system

The fuel system comprises items such as the fuel tank, pipe, valves, and pump. Corroded parts are always a problem in any vehicle because it prevents your gas from flowing correctly. The result of this problem is fuel leakage which causes a vacuum leak. It also contributes to rough idling in your Ford F150. 

You can fix it by replacing the corroded parts within the fuel system.

Make sure you have regular check-ups for corrosion in the entire fuel line from your tank, to the fuel filter, to your engine injector pump.

5. Idle speed not set-up properly

Idle speed is one of the most critical settings of your Ford F150 engine. We use it to control the engine RPM at a stop. The Ford F150 engine will run at very high RPM for its current driving condition at high idle speeds. On the other hand, when it is set low, the engine speed is low, and fuel consumption will increase.

It can be either set manually or electronically. 

When the idle speed is not correct, it can cause many problems including the up and down issue. We can fix it by checking the idle speed and adjusting it accordingly.

There are different ways to set the idle speed, and these include adjusting the throttle cable, adjusting the airflow meter, setting the idle voltage, and many others.

6. Faulty sensors

The idle speed sensor measures how fast your engine turns over to maintain proper idle speed or response. It is located under the throttle body and controls airflow.

The oxygen sensor measures the amount of unburned gas in your exhaust and optimizes fuel injection to optimize fuel efficiency and emission rate. 

When these sensors become faulty, they can cause rough idling in your F150, stalling, and high gas mileage. The best remedy to these sensors is to replace them since one cannot be able to repair them.

Handy Hint: Here are some tips on how you can get better miles per gallon from your Ford F150 by making small adjustments to your driving.

7. Bad distributor

A distributor is a crucial component in the ignition system, which is responsible for distributing the spark to the engine. It is located on the side of your cylinder head and has a rotor that rotates and powers to the spark plug. 

A lousy distributor will cause a Ford F150 idle up and down problem, interrupt the spark, and become weak. Replacing it is the best option I had. 

8. Ignition coil

The ignition coil delivers a high voltage to the spark plugs. A bad ignition coil can cause an idle problem or a misfire in an F150. It’s easy to test these coils by checking your engine’s ignition. You can also determine how well they are doing by checking the spark plug light and color.

If the engine is misfiring, check each coil to see which one is causing the problem and replace it.

Related questions

Where is the idle control valve on a Ford F150? 

The idle air control valve (IAC) on a Ford F150 can be found either on or near to the throttle body. 

How do you adjust the idle on a Ford F150?

To adjust the idle on a Ford F150, follow these step-by-step instructions.

  1. Open the hood.
  2. Locate the idle screw (find location in manual) – don’t adjust yet.
  3. Start your engine and let it warm up.
  4. Adjust the idle screw with a one quarter turn. Turn left for a slower speed, turn right for higher.
  5. Sit back in the cab and watch the RPMs. After 60 seconds or so you should see a change.
  6. Repeat the process until you’re happy.

Handy Hint: For more detailed instruction including what tools you need, read this guide to manually adjusting the idle on a Ford F150.

What is normal idle RPM Ford F150?

On my 1997 F150 4.2L, it tends to have an average idle rate of between 800 and 900 RPMs when I am sat at the lights. Normal idle with differ from model to model though.

I’ve explained in more depth what the normal idle RPM is in this post.


Image in header via CC license on Wikipedia: https://en.wikipedia.org/wiki/Ford_F-Series#/media/File:2018_Ford_F-150_XLT_Crew_Cab,_front_11.10.19.jpg

Josh Henderson

Hi I'm Josh and I'm a huge pickup enthusiast. I started this website in 2018 in order to share all my projects and custom mod tips that I've done with my own Ford F-150.

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