My 4Runner will occasionally behave weirdly when pressing on its gas pedal. When it happens, it is usually when at a standstill and then pressing the gas pedal to move forward doesn’t do anything, not even rev the engine up. The vehicle just idles forward, which is very dangerous if you are in an intersection and can’t move anywhere! (Note that the 4Runner starts and idles just fine.) This can be due to two possible problems. Either the Vehicle Stability Control (VSC) system needs to be recalibrated (the fix is described in one of my older posts), or the throttle body is dirty and is sticking shut (the fix – cleaning the throttle body – is described below).
When I first noticed the symptoms, I had no idea what was wrong with the vehicle until I found this discussion here. And then I found this helpful post explaining how to clean the throttle body. However, I found that there were other nuances in cleaning it, so I included those in my post as well.
You don’t need very many things to perform this fix. First, you need a phillips head screwdriver to be able to remove the air intake hose clamps. Second, you need throttle body cleaner (note that you should use cleaner that is specifically made for cleaning a throttle body, not for other automotive electrical or mechanical components). A toothbrush to help clean is advisable, but not necessary.
- Throttle body cleaner (aerosol can, made specifically for the throttle body)
- Tootbrush (optional, helps with cleaning)
The problem with the vehicle not accelerating nor revving the engine when the gas pedal is pressed is due to a dirty and sticky throttle body. The throttle body is where the air intake hose assembly connects to the engine. Air getting to your engine follows this path: Air intake → air filter → air intake hose → throttle body / throttle plate → engine cylinders.
Note that the throttle body assembly has two main components to it. First, the throttle body is the housing that contains other components within. Second, the throttle plate is a butterfly valve that allows more or less air into the engine when it is opened or closed, respectively. The problem I described above is that the throttle body and the throttle plate get dirty with black carbon gunk that makes them stick together so that the throttle plate temporarily cannot open. When the throttle plate cannot open, that means that the engine gets starved for oxygen so that the vehicle’s computer compensates by not feeding any fuel either. Thus, pressing on the gas pedal has no effect on the engine. Cleaning the throttle body and plate will allow the throttle plate to open freely again.
Getting to the Throttle Body
The first thing to know is the location of the throttle body. The picture to the right shows the location. It is where the air intake assembly attaches to the engine.
Next, to gain access to the throttle body and plate to clean them, you will need to remove the air intake assembly. See the picture to the right to see how to remove the assembly. It is quite easy, start at the bottom of the picture and then work your way up.
- Unclip and remove the large electrical connector to help free up movement of the air intake assembly.
- Unclip the small mechanical clip that keeps the electrical wire on the air intake hose. This is easy to do with either your fingers or pliers.
- Unscrew the lower clamp that keeps the rubber hose secured to the MAF sensor housing. You only need to loosen it enough so that you can fit a fingertip under the metal clamp.
- After loosening the clamp, separate the rubber intake hose from the plastic MAF sensor housing.
- Unclip the small hose that runs alongside the large air intake "muffler" (the big, black, plastic box).
- Disconnect the other small hose that connects directly to the air intake "muffler" (simply pull it off).
- Unscrew the two metal clamps up by the throttle body that keep the rubber air intake hose secured at the engine. One of these goes to the metal throttle body, and the other goes to a plastic tube (loosen both clamps so that a fingertip fits beneath the clamps). Then separate the rubber from the metal and plastic pieces.
- The air intake assembly should now be free to lift up and flip back over the engine. It is not completely detached, but it is enough to get it out of the way.
With the air intake assembly out of the way, you can now get to the throttle body and throttle plate well enough to clean them. Before you start spraying cleaner everywhere, first put some rags down below the throttle body opening to catch any excess cleaner runoff. The cleaner can ruin any rubber or plastic that it contacts. As you can see in the picture to the right, the throttle body is the metal housing. The throttle plate is the butterfly valve inside the throttle body. Go ahead and manually rotate the butterfly valve by pushing on it to see how it works.
Cleaning the Throttle Body
You can see in this picture (click on it to enlarge it) how dirty the perimeter of the throttle plate gets. Do you see all of that black gunk all the way around where the throttle plate contacts the throttle body? That gunk is what needs to be cleaned up because it can make the throttle body and plate stick together so that the engine cannot accelerate.
To clean it, spray a little bit of the cleaner on the black gunk. You probably will not be able to get it clean simply by spraying, so you will also need to either wipe it away with a rag or scrub it away with something soft like a toothbrush. I recommend using a toothbrush, it will be much easier. As you clean, also turn the throttle plate as you do it (see picture at right) so that you can get the areas of the throttle body that are behind the plate and so that you can get the backside of the plate, too.
When you are all done cleaning, there will not be any of the black gunk remaining. See picture at the right of the clean throttle body and plate. (Sorry that the picture is a little blurry.)
Now that you are done cleaning, remove the rags and reassemble the air intake hoses, clamps, and clips in the reverse order that you disassembled them. Don’t forget any of them! (I forgot one of them in this picture – can you spot it?)
If you can, wait an hour or two before starting your car. That way if any excess cleaner dripped down further into the engine past the throttle body, then it will have a chance to evaporate. If you were very careful when you cleaned it, then you might not have gotten any excess down there. However, I knew I had gotten some down there so I waited about 2 hours. After 2 hours the engine didn’t want to start for a few seconds, but then started right up after that and hasn’t had any problems since then. The original problem describe at the beginning of this post (the vehicle having problems accelerating on cold mornings) also went away.
Oh, and one more thing. Don’t use the toothbrush as a toothbrush anymore, throw it away.