It will F@#! your car up real bad.
You can tell a timing chain is bad when your engine makes a sharp washboard-like sound that increases in intensity when the engine's RPMs increase.
It uses a timing chain
it leaks oil
Normally it will become noisy.
it's no more timing belts on Sienna's since 2008.It's timing chain
how can you tell if a timing belt is bad
These have a timing belt . They stretch out and yours is old . If you can not time it or it is mis firing for no other reason , then it is most likely bad .
If you think it is going bad STOP DRIVING and get it changed immediately. If the timing belt/chain goes while you are motoring it will ruin the engine.
A loose timing chain should be replaced.
Timing belt or chain may be bad.
This does depend on the engine design itself. If it is known as an interferance engine, then it is possible that the pistons can hit the valves if the chain breaks in operation.
Bad timing/valves/rockers/timing chain