stumbling 4kcsq

[James D. Hanson]

My 87 4kcsq seems to have a problem... when accelerating away from a stop,
the engine stumbles between about 1000 and 2000 rpm.  Accelerator position
seems to have no effect.  If I rev the engine first a few times, then
accelerate, there's no problem.  Similarly, if I don't give it a chance to
settle into idle, its fine.  This happens warm and cold, though its most
noticeable when the engine is warm.
Any ideas what is causing this?

Thanks,
Jim