My 2000 toyota sienna accelerates suddenly without pressing the gas pedal.

Do you mean the engine will not rev up when the gas pedal is moved

How old is your vehicle....most common problem is throttle position sensor...

Transmission band slipping.

You didn't say what year it is but on later models,2004 and up there is a fuse for the throttle control, check in the box under the hood for a fuse marked ETCS, try a new fuse in it's place.

WD 40 all over what you can see inside then from the under side as well. probably has build up on it ,just needs cleaned and loosend up.i had one stick on me one time because of it .

That's a possibility, but before you investigate that, as it's a smaller possibility, please check the following:
1) Spark plugs, leads and coil(s)2) Fuel filter and pump3) Air filter.
Those are the more probable issues which often cause faults such as this.

possible clutch failure --sounds like clutch is slipping

I know this might sound dumb, but it has happened to a lot of people - make sure your floor mat (not even a corner of it) isn't on top of the accelerator pedal. Even the slightest weight can cause the pedal to accelerate enough to be noticeable.
Not dumb, it's a good answer. The floor mat can slip forward (and has) in two of our new vehicles when we were driving on the highway. It had worked its way off the anchors and slipped forward, causing the vehicles to accelerate. I put the gearshift in Neutral, pulled off the highway and that was the problem, both times. I don't think it was on top of the gas pedal, underneath, but still pressing or I guess, pulling the pedal down.

All of these are good answers, but if it's an automatic transmission, it might be normal provided the engine performance is ok. Auto trannies have a torque converter stall speed. I have a 96 Cadillac Fleetwood and it will move on its own.

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I have a 2004 Toyota sienna some time my gas pedal wont go why can you tell me what I can do

Hello, Zman777.

According to the material provided by Toyota, the Denso pedal does not have the alleged acceleration issue.

Also, according to information that has been provided by Toyota, the alleged acceleration issues is being caused by two possibilities;

One is additional placement(s) of floor mats on top of the factory floor mat. The extra mats are not secured, and can move around the driver side footwell, and, in the worst case scenario, move on top of the accelerator pedal, and trap in into the 'applied' position. I myself have experienced this mat/entrapment issue during a road test.

The other possibility is that certain accelerator pedal mechanisms may mechanically stick in a partially depressed position or slowly return to the idle position. Over time, the internal mechanism in the accelerator pedal my become worn. As a result of this wear, combined with certain operating and enviromental conditions, friction in the mechanism may increase and intermittantly result in the accelerator pedal being hard to depress and/or slow to return or, in the worst case, stick in a partially open position, increasing the risk of a crash.

In short, according to what we have been provided, the issue is mechanical, not electrical. The modification that Toyota dealerships are performing rectify this issue, and, this modification has been approved by the NHTSA.

Nowhere has it been found that the vehicles with the alleged acceleration issue have 'accelerated' without warning, as in sitting still, and the car is suddenly going 100 mph. None.

What 'could' happen, if the pedal 'was' sticking, is, in my opinion, an 'Unexpected Non-Deceleration' condition.

If you were going 15 mph, and the alleged issue appeared, when you let off of the gas pedal, the car would continue at 15 mph, and NOT accelerate to 100 mph, as has been falsely mentioned in the media.

Regarding VW, sorry, I cannot comment on VW, or any of their systems, I am not a certified VW mechanic.

I hope that this info helps you out.