One problem related to tire valve has been reported for the 1998 Toyota Sienna. The most recently reported issues are listed below.
Loud bang from egine followed by fire. Dealer says engine threw a rod and found hole in engine. Also damage to right axle from projectile from engine. Complained about white smoke at startup to dealer at 22,500 mile service, but dealer found no problems. Now dealer refuses to honor warranty claiming that sludge is in engine. When I had similar smoke problem with 1998 Toyota camry, dealer advised that the valve seals were defective and replaced the valve seals and gasket under warranty. Internet serches have revealed at least one and possibly as many as three other similar engine failures due to sludge after complaints were made to the dealer of white smoke at startup. I also found multiple reports of engine failure assoiciated with white smoke at startup when doing searches regarding the camry. When I went to dealer to remove articles from the van after it was towed, the service advisor pointed out the left rear tire, on which approximately 10-12 inches of the tread had separated from the body of the tire. This is firestone fr 680 tire with less than 30,000 miles on it. The tire was checked and was fine prior to out trip to pick up out eight year old daughter from summer camp. The engine failure and fire and the separation of thread of the tire occurred after we had driven for approximately 2 hours in 100 degree plus temperatures while returning from the camp. Local police and fire department was called to the scene. ( dot number: ).