I recently picked up a 91 RX7 that is having a few issues at the moment. First a brief history on the car. The person before me purchased the car as a shell, and installed a S5 engine in the car, but he wasn't able to get the car to start. Since I got the car, I have been able to get it to start, but the car will die unless you keep the engine running higher than 2000 rpm. It seems like before car became a shell, it had a S4 engine in it since the pressure sensor is marked as N327, as well as the variable resistor.



My question is will a S4 pressure sensor work with an S5 engine, and if not, is that the reason why my car won't idle properly? I have checked for vacuum leaks, but I haven't been able to find one yet.

the s4 sensors are the same as the s5 ones, but they added an extra pin on the s4's for a 12v signal. so if you want to run an s4 sensor on the s5 ecu/wiring, you need to run the extra 12v to the 4th pin.

I assume you are talking about the 4th pin that is currently empty? Can I just splice into the 12 volt wire for the pressure sensor if there is one?

yes and yes

I probed the three wires on the s5 plug and I got: 5v, 0V, 0V. I think one of the 0V is the ground going to the ECU, the other is supposed to be terminal D which is supposed to read about 2.5 volts or so. Would the 5v signal that I probed the voltage for the pressure sensor? I can't seem to find a 12v signal in the plug for the pressure sensor...

the difference between the s4 and the s5 is that on the s4 they use the 4th pin and it has 12v. if you have an s5 car it does not have a 12v signal there, so if you want to use the s4 sensor you have to add it