Hi, I recently installed some parts:
Evo X LICP
Evo X IC
Evo X BPV
Nisei 2 piece UICP

Initially everything was fine, but now the car just keeps idling down and sometimes just shuts off at low idle if I don't press on the gas . Any help troubleshooting would be appreciated. Could it be a leak? Or what else?

 

Check all vacuum lines for leaks. Just in case you might of bumped one. Also check the intercooler pipes that you installed and make sure there is no leakes in the connections.

 

X2 for vacuum line issue.

 

There is an air leak somewhere.

X3 for the vacuum line or leak issue.

Also, reset the ECU. Remove battery terminals for 15 mins, reconnect, turn on car, let idle for 5 mins, shut off, turn car on, go drive nice for 50 miles, then proceed to pound on it like normal.