RX7 FD RPM JUMPING

Hey there, my rx7 fd has a bridgeport single turbo setup and its been RPM HUNTING sometime at idle and all the time when i hold the throttle steady even on the dyno...TPS readings are less than 1 volt however i replaced the entire tps and same problem...any thoughts? Maybe the replacement throttlebody i got is shot aswell?

uh, that's what bridge ports do....

Bridge port engines do tend to be somewhat unstable at low airflow as David eluded to, but have you tried altering fuel mass delivered and fuel injection timing to see if that helps?

This can somewhat be tuned similar to a big cam piston engine, which HPA does have specific info on, in that the timing of the port injection is important, and you may need a bit richer mixture than you're used to in order to achieve stable operation at low airflow.

There's also a rotary tuning example within the Practical Standalone ECU tuning course.

As the others have said, it's a basic characteristic of that engine and modification - the problem is a poor air-fuel mixture and, possibly, exhaust dilution.

As Mike suggested, playing around with the fuelling (it often needs an over-rich mixture) and timing if the injection so it's at the highest velocity period in the port, should help.

If it's really annoying, you MIGHT get some benefit from bigger spark plug gaps - needs a GOOD ignition for higher boost, though - or maybe one of the multiple stike CDI systems would help as that gives multiple spark plug firings per cycle, which increases the odds of at least one causing the fuel-air mix to ignite.

Are you still phasing the spark plugs or firing them together? Might be worth some experimentation there, too?

Bias to more air and less ignition timing to soften pulse generally around idle/light load.

The most common QoL issue that people bring me for their self tuned (or even uninformed professionally tuned) rotaries are idle issues - usually due to too much advance in those cells + no smooth transition. 0-4* is generally my go to starting point.

Hey guys thanks for the feedback...will take notes of what yall said. However i understand how the bridge idles and revs but it isnt the bridge sound itself making the issue...the bridge sounds fine once its not hunting and while reving its always jumping...will look into the map

Will probably idle happiest somewhere around 12.7 afr petrol scale.