I'll start off sayin i have a 2000 Z24... heres the problem. I take the highway to work. After 20mins i get off and when i hit the end of the ramp sometimes i gotta stop at the red light. When i do, and in 1st gear, the rpm's go up to 1500 back down to 500 back to 1000 than they drop right out and the car stalls. Only done this twice in last 2 months. Any ideas why?
EXACT same thing happened with my 2000 z24. I replaced all vacuum lines and cleaned the throttle body with carb cleaner while I was at it. Seemed to work after that. Mine would jump around on the RPMs and then stall out while I'm stop in go traffic after driving for awhile. I had my sensors all checked and everything was running fine. My sensors could have been gummed up with carbon build-up or one of my hoses seemed to be brittle and cracking. Try that first.
Manual or automatic?
Mine will do this a few times after disconnecting the battery. Once it "learns" how to idle again, it stops happening. It's as though it's not expecting the RPM's to drop as quick as they do and isn't able to catch it in time before stalling.
I would second a good cleaning to start with. Make certain to remove your IAC and give that a good cleaning outside the TB. If that is sticking you could experience this issue. If that doesn't work, then I would go back to Weasel's question.
manual.... a friend at work mentioned it may be the IAC
Clean the IAC but do NOT push on the pintle.
Also you can re-set the IAC after you clean it, disconnect the battery for 15 mins and then reconnect - put key forward twice to let the IAC re-set itself.
Something is stopping the IAC from opening in time to catch the idle... so a good throttlebody cleaning and once-over of all the lines and sensors should do the trick.
Slowly but surely may some day win this race...