My 1999 Toyota Sienna takes time to start and when I press accelerator it goes off

welcome, when your car is cool you start it to go, so firstly you leave the for almost 5 minute in start position. Then you will go easily by pressing the accelerator, it can't goes off. but it doesn't go through this then the problem is in your car engine consumption of fuel. The fuel is not coming to engine properly. In the way of the fuel, there is some rubbish which can't leave the fuel to came to the engine properly. So when you press the accelerator, it goes off. so kindly, check the transaction of the fuel of your car engine.

Given the trouble starting it I'd be inclined to say it's a bad ignition coil.

Another possibility is the torque converter locking up (surprisingly common on 90's Toyota auto boxes)...but that wouldn't explain the starting troubles.

I would check, clean or replace, the mass airflow sensor or map sensor. This is what tells the car how much load is on the engine if this value is wrong it can and will exhibit the symptoms you have. Moreover, it may not trip the engine light if the sensor is just out of spec and not burnt out. As this sensor is used to check values that naturally change quickly.