hmmm, a bit strange. My Carrera idles high on cold start for a minute or two, but then settles to 850rpm's or so. I don't know much about the CIS systems, but sounds to me like you have a dodgey WUR (Warm Up Reg)? Hopefully someone more CIS-savy would tune in here. Good luck!
'89 911 Turbo Cab
Protomotive MAP ECU, Twin Plugged Heads, GT2-EVO CAMs, 3.3L fully finned P&C's, ARP fasteners, C2T head gaskets, Titanium Retainers, Turbo spec valves, springs & guides, 964 splash valves, GT35R BB turbo, GSF Stainless Headers, Magnaflow Exhaust, Full bay Intercooler, TiAL 46mm w/gate, TiAL 50mm BOV, Apexi AVC-R EBC, SPEC Stage3+ Clutch kit, Crane CDI Ignition