I have a rebuilt 90 5.0 in a 90 Miata. If you keep your foot in it and run through the gears car runs like a raped ape, but when you get out of it it stalls. It also stalls randomly at idle, I can let it sit until its warmed up and it will just die. It always fires right back up. After a wide open throttle blast it will die upon returning to idle, then and only then is it hard to restart, it acts "flooded" and you have to to blip the throttle to get it to stay running, and it will hunt for idle for 10-15 seconds, this leads me to think ignition, instead of fuel, because its still fueling when it stalls after WOT or it would not act flooded?, It always restarts and will run. I just bought this car. It had a bad TFI which I replaced. Fuel pressure is at 42-45 psi at idle, I dropped it to 38 but it ran lean so I bumped it back up, wideband showing 12-14 af.

Ive tried it with the SCT chip on stock, 14 TDC and 12 TDC setting, doesn't seem to matter. 2 step is turned off.



5,0, A9PEEC, 24lb injectors, 24lb MAF, INNOVATE wideband AF meter, AEM inline pump, mystery (knock off Aeromotive) regulator, GT40X aluminum heads, SCT switch chip, Comp cam, Pro Comp 1.6, Pro Comp Upper and Lower intake, MSD 6AL, MSD Billet Dizzy, MSD Coil, MSD 2step, NX Plate system, Summit window switch

 

Sounds like you need to clean the throttle body & IAC valve, & then set the base idle.

 

What tbone said. I would also look to see if there are any EEC codes. Even with the SCT chip, it should provide any appropriate codes (I would hope!)

 

Mine did that when I had a vacuum leak.
TM

 

I agree with TopDown . . . sounds like a vacuum leak. Look for a hanging vacuum tube under the hood somewhere.