Bit of background first: had the carby fully rebuilt while I had the old girl off the road repacing the head gasket. Before the ute was taken of the road the idle would jump up and down as it was sucking in way too much air (carby and gaskets were shot). When I pieced the ute back together there was no issue, other than having to remove the idle control solenoid. That was until....

Yesterday while in heavy traffic the ass suddenly fell out of the idle, dropped from 800rpm to 200rpm. After that it was inconsistent, settling at different speeds as I came to a stop, from as high as 600rpm to as low as just off stalling.

Why would it be doing this? The ute has been running well for over a month now and it just happened out of nowhere. I really thought I was over fiddling with this thing.