My Sienna's Got the Shakes!

At around 30mph and higher, my 2004 Toyota Sienna starts with a constant vibration coming from the front end. It gets faster as the speed increases and it only happens when I’m accelerating… when I take my foot off the gas it goes away. I unknowingly bought the car with this problem, and I’m trying to decide if it’s worth it to fix it or sell as is, but I’m getting stumped about the cause. A couple mechanics thought it is from bad motor mounts. I replaced the front mount because it was the easiest to access and could clearly be seen as cracked in the rubber. However, it didn’t seem to change the vibration at all, and my mechanic then wasn’t convinced that spending money on trying to replace the other mounts was going to do the trick. Another person took a look at it and didn’t think it was the motor mounts either, but thought it was something in the drive train which would need to be checked out by the dealer which would be fairly costly. I would love to get it fixed because the rest of the minivan is in good condition, but I’m not sure how deep into my wallet I’ll be getting. Any advice would be most appreciated!

Sounds like a failing CV shaft (axle shaft). Any reasonable competent garage should be able to diagnose this for you, and if it does need an/both CV shafts they’re not very expensive.

I think you need new spark plugs and/or wires.

Siennas do not have spark plug wires. I think they physically connect to the plugs.

I agree with asemaster.
More than likely, the inner CV joints are to blame, and replacing both axle shafts should remedy the problem.

However, because your regular mechanic seems to be stumped by this situation, I recommend that you seek a new mechanic in order to confirm this diagnosis, rather than just throwing parts at the situation. If you use the Mechanics Files link at the top of the page, you can search for recommended mechanics in your zip code.