Q: Bucking

asked by on December 10, 2016

Truck bucks while going up a slight grade and hitting a bump,does not do it while using the cruise control

My car has 116000 miles.
My car has an automatic transmission.

This may be a sign of a faulty MAP sensor. 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 (spark knock) 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 replace your MAP sensor.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

No power to the fuel pump. 2002 Ford F150

Hello - check for a voltage drop coming out of the [fuel pump relay](https://www.yourmechanic.com/question/is-my-fuel-pump-working (in the battery junction box/fuse box underhood). That is the one link in the electrical path you don't mention checking/replacing. A failed fuel pump relay may...

How are MP3 tracks and folders organized in the audio system?

Your car’s audio system is capable of recognizing MP3 files and folder when loaded on a CD-R or CD-RW. It offers two different ways to play those files: Track Mode: This is the default method. The system will automatically...

My car has a high or surging idle

Hi there: The throttle position sensor is the most common component that causes similar idle issues you're experiencing, so it makes sense that replacing the TPS might be a good start. However, other issues could include dirty throttle body or...

Related articles

The 5 Safest Used Cars You Can Buy For Under $20,000
The Subaru Legacy, Honda Accord, Ford Fusion, Chevy Volt, and the Volvo XC60 are five of the overall safest used cars you can buy for under $20,000.
The Best Used Cars to Buy If You Just Had a Baby
Having Having a baby will completely change your life. Your activities and hobbies will change. Your sleeping patterns will change. Chances are good that you’ll also be looking for a change in vehicles. You need to ensure that your car...
The Best Used Cars to Buy If You're a Farmer
If If you're a farmer, you know that what you need isn’t a used car – it’s a used pickup truck. How else are you going to haul around hay, implements, garden produce, fertilizer, and all the other things you...