car idles roughly after being drove a while

I have a 1983 datsun 280zx with 110k miles.After being driven a while the car sometimes idles roughly and tries to die so I have to race the engine to keep it going .it doesn't do this all the time, mainly noticeable on warm days after being ran hard.I recently changed the distributor but the new ignition module was bad so I had to use the old one.It had however been changed apprx. 25k miles ago.Thanks for any help you might offer.by the way this is an L28 non turbo motor.