Two problems related to engine have been reported for the 2008 Toyota Sienna. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2008 Toyota Sienna based on all problems reported for the 2008 Sienna.
Driving my 2008 Toyota Sienna and it felt funny and I heard some rattling from under the hood. No idea what the problem was but I knew that something was definitely wrong. I checked the oil and the dip stick was completely dry! I put in a few quarts of oil and it came out all over underneath the car as I was driving. Had it towed to the dealer- they told me it was a faulty rubber oil line. I looked it up online and see that Toyota had not yet issued a recall but is replacing it in some vehicles. The 2008 Toyota Sienna is not mentioned - but clearly should be. This is a van that I drive my 2 children around - very clearly a safety issue if I did not recognize soon enough that the engine had no oil!.
In the summer of 2009 my Toyota 2008 Sienna xle awd engine speed slowly started to climb without my foot on the gas pedal. I don't remember the exact sequence of events that followed but I believe I placed it into neutral, stopped, placed it into park (automatic transmission) and turned the engine off then on again. After that the engine responded only to my actions on the gas pedal. It did occur to me that the pedal could have been caught under the floor mat so I checked its position and it was some distance from the pedal and could not have been the cause. I have owned this vehicle from new in may 2008 and this undirected acceleration has only occurred once. The car has just completed 20,000 miles. I reported this to the dealer who serviced my car for the 20,000 mile interval and via Toyota's web site but I want to make sure you are aware that Sienna vans can also have this problem.