How to Troubleshoot an Idle That Is Going Up and Down in an F-150

by Sameca Pandova
itstillruns article image
Thinkstock/Comstock/Getty Images

A uneven idle on a F-150 can be a symptom of a variety of engine issues such as vacuum leaks, failed or dirty sensors or worn engine components. If the engine is older or has higher miles on it, the typical culprits will be dirty sensors and carbon deposits on engine head components. Finding the ultimate cause of an uneven idle can be a trial and error process, but a cost-effective way to cure your F-150's idle problems is to start by cleaning specific components to see if this restores a smooth and even idle prior to replacing components.

Step 1

Remove the mass airflow sensor from the intake duct and clean it with MAF sensor cleaner available from automotive parts stores. Do not to touch the sensor itself. The MAF informs the engine computer about the amount and the temperature of the air in the intake. When it gets dirty, it can cause a poor or incorrect reading that affects engine performance. On the F-150's 4.6-liter V-8, the MAF sensor sits in the intake tube just after the air filter, secured with two Torx bolts. Spray down the MAF sensor, and then allow it to dry before reinstalling.

Step 2

Remove the air intake tube by releasing the stainless steel clamps that secure it to the throttle body and air filter housing. Spray throttle body cleaner into the throttle body opening, and hold the butterfly valve open to spray the interior of the housing. Use a soft cloth to clean the throttle body after you have allowed the cleaner to work for a few minutes.

Step 3

Use a top-end engine cleaner to clean carbon from the engine. With the engine running, remove the brake booster vacuum tube off the brake master booster, which is the large oval canister right in front of the driver's position on the engine firewall. Gently feed a small cap of engine cleaner into the engine, and then turn off the engine and allow it to sit for 20 minutes.

Step 4

Restart the engine and go for a spirited drive. You will see a large amount of white smoke coming from the tailpipes -- this is carbon. Repeat this process again to remove any additional carbon buildup. Add a can of the appropriate cleaner into the gasoline tank, and then add a half can of an engine cleaner into the engine crankcase. Change your oil after driving about 200 miles. Time this process on schedule for an oil change.

Step 5

Use a steel wire brush to scrub clean the battery posts and the battery terminals on your F-150. Oxidation and rust contribute to poor electrical connections and can cause unstable sensor readings. After cleaning the posts and terminals, spray them with lithium grease to help protect them from oxidation or rust.

More Articles

article divider