After going down the very long and expensive road of troubleshooting of why my EJ22 would idle on 3 cylinders I found the issue to be the (infamous) Jideco ignition relay. Many hours of searching showed this as a common issue but the only resolution I've seen so far was to replace it with another used item of questionable condition or try and find a brand new one.
I have a solution for this which replaces the old Jideco relay with a pair of readily available aftermarket relays. Digging through some cars at a wrecking yard I found a common trend among ones with faulty ignition relays. Generally all pre 1992 models with AT seem to have this issue, in fact every one I have ever come across has shown signs of this problem. I own a manual pre 1992 model which does not have the idle issue. Among the few cars I saw in the wrecking yard, all series 2 AT models still had the original relay. If anyone can offer any more information on this please let me know.
Anyway, one can simply replace the Jideco relay with a pair of suitable aftermarket relays. I have used two Bosch 0 332 019 150 relays, these are 12V 30A relays and can be had for around $8 each. Just neatly make yourself a set of blade terminals and you can plug them straight into the caramel coloured factory relay plug.
I have been using this setup for almost two weeks and have had the benefit of testing it in various weather conditions and it's worked perfectly.
Wiring Diagram
Bosch Relay
Relay Internal Diagram
Terminals, I just taped the relays together
Ignition Relay Plug Side
. Lifted, bars, exhausts... View 
don't let them do the job but ask them as many questions about the job as you need too.