Because there was SO much intake cleaner in the system, and so much freed up gums, varnishes, etc, when I started up the car, I had to crank for much longer, when it eventually caught, the rpms went up to about 2400rpm, and there were all kinds of weird sounds the engine and exhaust were making, as well as a tonne of black smoke coming from the tailpipe. Basically, while cranking, the engine would catch, then die, and catch, then die . . . until it finally caught.

The Kleen-Flo product I used was an intake cleaner designed to clean all the ducting as well as the throttle body, and intake manifold. It explicitly states that it is O2 sensor and catalytic convertor friendly.