[Brian R.]

Welcome to the AF!

There is a Toyota Service Manual for your engine at the top of this forum in a sticky post.
Here's a start (top is most likely-easiest, bottom less likely-hardest IMO):
1. Check for vacuum leaks in hoses-bad connection, cracks
2. Check for bad electical connections on ignition system
3. Check your engine coolant temperature sensor and electical connection. <= My guess
4. Check your heated oxygen sensors (the ones closest to the heads) <= My second best guess
5. Clean the EGR valve
6. Check EGR Gas Temperature Sensor and VSV
7. Check EVAP VSV
8. Clean the IAC valve and throttle body