free rev hesitation at 4k rpm?
 

87' Turbo II. S5 keg with S4 electronics. Currently have broken AIT sensor and all other sensors are fine. Have an SAFC (old school one) with an unknown tune. Seems to drive fine at all rpm's. But when warmed up the idle pulses (no porting here) and when i open the primary tb plate only right around 4k rpm it loads up and spits black smoke and freaks out...

Any ideas?

No vacuum leaks, all emmsions removed, tb 100% cleaned up, no BAC, pretty much bare bones....

Fixed hesitation. Put all settings on SAFC at zero. And idle is still whacky. It pulses from like 900 to 1400. and when i give it just a touch of throttle it still pulses. and at like a steady 2k rpm it sounds like its missing really bad. But everything above 2k is great. revs fine and no smoke...

That's why it idles poorly. Do you even know why engines have idle air control valves? Not like it adds weight or hinders performance, it's so the damn engine will hold an idle.

Anyways, did you also happen to remove the throttle position sensor when you 100% cleaned up the throttle body? If not, check it to make sure it's sitting at 1.000 volts at idle fully warmed up. Look in the factory service manual under the emissions section, it'll tell you which wires to tap into to find that. Incorrect TPS settings are about 70% of all the Rx-7 idle issues. Other things are vacuum leaks, incorrect timing, a worn out airflow meter (yes, they do wear out since it's just a rheostat connected to a flap), old fouled spark plugs, ECT sensor failure (will have more problems than just at idle though), or someone messed with the variable resistor and now the idle map is too lean.

If your SAFC is connected properly, it should show you voltages of the AFM and TPS. Just adjust it until that voltage reads 1.000. Rev it a few times, try again. Keep adjusting and revving until the closed voltage consistently reads as close to 1.000 as possible. Don't neglect to check the timing and set the idle to 750 rpm with the initial set coupler jumpered.

And replace the AIT sensor.

TPS is 100% fine. Along with all the other stuff you said. already checked everything. Just need to do timing but its not more that 1 or 2 degrees off. Just cant figure out idle!!


Probably could clean AFM and get new plugs. And no AIT sensor...