Miata Turbo Forum - Boost cars, acquire cats. - HELP: NB-NA Swap, Squaretop Manifold Vacuum Routing/Random Misfire/PRC Solenoid Valve

Hi everyone,

I swapped in a 99' motor into my 97' NA last year and am having trouble passing emissions this year due to a random misfire (P0300) that keeps coming up. The car runs perfectly fine on megasquirt, and was tuned properly last year. However, since emission requires me to have my stock ECU in, I'd need to get my CELs sorted out in order to pass.

The car is unable to idle well under 1000RPM (even on MSPNP it likes to stay around 1200RPM at idle). Specs on the car:

97' ECU/harness
99'motor with 97' electronics
JDM Squaretop manifold
BP5A Mazdaspeed intake cam
RB header
Test pipe
Racing Beat Catback exhaust

Things i've replaced so far:
-Throttle body with new IAC and TPS
-O2 Sensors
-Spark plugs
-CAS
-Crank position sensor
-Coilpack
-Ignition Coils
-Spark Plug Wires
-Fuel filter

With that being said, I noticed on the wiring diagram under my hood shows that there should be a vacuum hose coming from the FPR that connects to a 3-way solenoid valve. Currently, I have a vacuum hose going from the FPR into one of the nipples on the intake manifold. I have no idea what the 3-way solenoid valve is, nor can I find a loose harness anywhere that it would plug into. From what I've read, its also known as the PRC solenoid valve.

Can anyone show me what the 3-way solenoid valve looks like and where it mounts? Could this possibly be the reason for my misfire? In addition, can anyone with a 96-97' please share some pictures of how their vacuum hoses are mounted, especially if they have the same swap as I do, or have a JDM intake manifold?

If it helps anything, Ive also been getting downstream O2 sensor readings of anywhere from 0.03-0.06V.

Thanks so much in advance!