I bought a 1999 4Runner a few months ago. 3.4L V6, Auto, Sr5 with 90K miles. I have been noticing that during starts (particularly when the motor is up to operating temp, say when running quick errands) that the motor stumbles at startup. It needs to crank slightly longer, and when it does fire up, it is not a robust start with the RPM shooting up. The tach dips, the motor nearly dies, and then stabilizes. The best way to describe is a bogging. A couple times, the motor has died, requiring a restart.

Also, not sure if it is related to this issue or what, but the truck has a rougher idle than I had expected. The noise the motor makes almost has a bit of oscillation to it, as if the RPM aren't staying constant, and actually dip up and down rhythmically.

Any others having these issues? What could this be related to? As an aside, the truck is due for its timing belt service, but I can't imagine why that would cause this symptom.

Just sounds like a dirty IAC. All you need to do is remove it from the vehicle and clean it out. While your at it, clean the throttle body. 2 things that will really improve the performance of the engine IMO.

Re: 3.4L V6 Hard Start "hot" Cleaned IAC (Pics) - YotaTech Forums