So, I've had this problem for awhile, but I've tried many different things that you would have thought would have fixed it with absolutely no luck.

I've read up and down on this forum with no luck, everyone has rough idle issues, but none seems like mine.

So here's the symptoms:
1990 Mazda RX7, swapped S5 TII (bought it from an idiot....)
All that's it's got done is an intake and a straight pipe, no emissions.

When you start it, it just shakes, idles rough, my tach doesn't always work so I can't even say where exactly it idles, but my vacuum on my boost gauge shows it going up and down. Popping or what everyone calls "Afterburn" out of the exhaust. But it will idle, then drop, then raise, then drop, and etc... over and over.
This problem occurs both at cold start-up and even after the car's been running for some time. Sometimes, used to do it more often, when I glide to a stop in neutral, the car will just stall itself, no clutch pedal depressed, just coming to a stop.

I've put a smoke machine on the car plenty of times. Found countless amounts of leaks: Inlet duct, vacuum caps from where emissions must have been blocked off, and gaskets.
So I've replaced the inlet duct, sealed the vacuum caps, replaced the upper intake manifold gasket, scoped the tps, checked voltages on the bac, everything checked out with no problems.

I brought it to school again to smoke it , because everyones been telling me it has to be a vacuum leak. We smoked it. Nothing. So I have no choice but to rule out a vacuum leak.

I've been researching this for awhile, I know that my fuel pressure is lower than it should be, need to replace the pump, but I wouldn't think that would affect the idle that much.

Any ideas would be greatly appreciated.

Thanks,
Shaina