I recently completed gen3 swap into a 1990 JDM turbo and a couple of small issues need resolving.
 
The idle is a bit high, around 1000rpm, maybe a smidge higher, when warm.  if air con is switched on it drops to 750-800rpm.
 
When warming up it sits nicely at about 1500rpm but occasionally flares to 2000rpm for a few seconds.  Also has flared for a couple of seconds to 1500rpm or so when warm just after starting, only done this a few times.  
 
Other issue is that the boost is on the factory safe/low setting of 0.6bar.  It builds boost from just over 2000rpm so I wouldnt think its a jammed open waste gate.  
 
Car has free flow intake, 3 inch dump with cat (ebay SARD copy) and free flow exhaust.
 
I have not connected the factory post cat temp probe as it is corroded badly into the cast iron and wont budge.  I wanted to substitute a resitor in its place and tried measuring its resistance when cold but it it slowly climbs until maxing out on the meter.
 
Any ideas on where to start looking?
 
Cheers

Intake leak? Air gets sucked in on idle causing it to rise, boost escapes whilst driving.

Hmmmmm... wouldnt think so, not for the boost anyway, the boost is too exactly regulated at 0.6bar for it to be a leak I reckon.  
 
Re the idle, its almost like it is acting in reverse, ie with air con it is low as should be normal, and normal is slightly raised as you get with air con engaged.
 
I will re check the hoses though to be sure.
 
Cheers

The way the aircon system works in a gen 2 is the complete opposite to a gen 3. The signal from the aircon amplifier to the ecu is what is confusing the ecu. For example the ecu is expecting to see 12v on that wire when the ac is switched on but with the gen 2 ac amp it puts out a ground (-) when the ac is on.
Anyway the above is probably not exactly correct but its something like that. I had the exact same problem on my old SW20 many years ago.
 
This can be resolved double pole relay.
 
Have a read on mr2oc and somewhere on there I think they mention exactly how to fix it. I just worked it out at the time but didn't write down exactly how I did it.
 
Hope that helps.
 
 

Ahhh, that is probably the issue.  Will suss out what the wires are doing and like you say can install relay to swap over the operation.  
 
Did a quick search on mr2oc but nothing of value came up, will keep searching.
 
Cheers

The low boost is fixed.  The issue was the ECU was not getting the speed signal, and was activating the safe low boost.  This was due to the HKS speed defender not being powered up.  Getting full boost now, close to 1 bar or just under.
 
Cheers