Individual coil on plug, ECU outputs logic 5V signals for each cyl.
  • 5V signals go to power transistors mounted in engine bay, these drive the individual coils
using the same, putting out 5V logic signals


lowZ injectors with dropping resistors mounted in engine bay
need possibility to drive either highZ or lowZ-s injectors, so "active flyback" option required
Q: do low-Z injectors still need dropping resistors?

Idle Control

no idea, probably the same as any other Japanese vehicle from the same era, 2pin terminal, 12V PWM
using the same
  • I would suggest to replace it with something simpler - i.e just one PWM valve. The original system contains 4 separate items: 1) A mechanical valve that closes when the coolant heats up; 2) A mechanical screw for adjusting the base idle; 3) A PWM valve that only changes the revs about +-200 rpm when hot (too little to use just that); 4) A valve for extra air when A/C kicks in.
  • Thanks for the info, didn't know the idle valve was too small, now I get why all that extra mess is there. I've planned to get rid of the on/off AAC (no A/C) and the mechanical air regulator, too.
    • How about running both IAC and AAC off the same PWM signal? Would that work and have the capacity to regulate idle across the whole range? (I don't want to buy/build anything extra I don't necessarily need.)
    • Or, is there a cheap, off-the-shelf or junkyard idle air valve from another make/model that would work in place of the mech. air regulator? I could install that in the parking lot.
      • Seems like a BMW M43-M50-M52 idle valves would almost work, except one of the 2 air hose diameters are not the same, as the CA18 air regulator. Would have to stretch the silicone over it.
Most engines have suitable idle air valve:

Fuel pump control

low side switch
using the same

Questions so far:

Flyback type: which one for lowZ, lowZ+R, HighZ?

ETC: for 2wire ETC, where is the 2nd wire connected?