Low idle speeds can be caused by a number of culprits, and the troubleshooting can be extensive.  Typical culprits can be as varied as:  intake vacuum leaks, too little fuel (lean), too much fuel (rich), bad spark (ignition), etc.  Best suggestion is to get a basic tune-up done first to eliminate most of the abovementioned possibilities.
FC3S Pro - FAQ, Basic Tune-Up

Before trying anything, make sure the engine is in good shape.  A compression check is highly recommended to ensure you're not messing with a hurt motor.  Low compression will cause a bad or low idle.
FC3S Pro - FAQ, Compression Testing

In most cases, it is intake vacuum leaks that is the most likely source of the problems.  For a more detailed description of intake vacuum leak troubleshooting, please click on this link:
FC3S Pro - Problems #1, Engine, Intake Vacuum Leaks

For possible fuel problems, check the fuel system to make sure everything is properly working.  Fuel injector cleaning is highly recommended if fuel injector condition is unknown.  Replacing fuel filters is also recommended if condition is unknown.  Zenki FC turbos have an idle mixture adjust screw that should adjust fuel delivery at idle speeds.  This idle mixture adjust screw is located on the passenger strut tower in the engine bay.  It is labelled "R" (for rich) and "L" for lean.  Adjust the screw until idle speed is highest.

Moving to the ignition system, bad spark plugs and spark plug wires can cause bad ignition spark, which will affect idle quality.  Bad or dead coils (packs) will affect idle quality.  Ignition timing off of spec will affect idle - usually too retarded.  Ensure spark plug wire position is correct!  The L1 and L2 spark plug wires are the bottom positions; swapping leadings front to rear does not change anything - both fire at the same time.  The T1 and T2 spark plug wires need to be in the correct positions.

Questions?  Comments?  Send mail to:  reted@fc3spro.com