Gerry,
Sorry if my comments about your setup sounded harsh, didn't mean to be that critical. The setup in general is great, with impressive grip on the rollers. The cooling side of things is more to do with the odd type of car that I have, and a little more experimentation would solve how to run it more effectively. I don't claim to have a normal car....
I would be interested in more details about the speed control loop, and am willing to help in solving the problem.
As to the actual cause of the problem with my car, I would put a fair amount of money on the fault being that my alternator and wiring is not up to much, and when you tried to calibrate the system it could not properly detect the current pulses from the alternator as the load you applied (lights and fan) were probably taken mainly from the battery. To overcome this problem, using a lighter load would probably fix the issue (ie. no lights/fan). Also the fan load probably caused too much inductive interferance.
You do need some load to help supress the noise coupled into the system from the ignition, but too much will swamp the alternator pulses. An alternative fix would be to have moved the point you connected to the system over to the alternator rather than at the battery terminals. This is tricy on most cars though.
Anyhew let me know if you would like any assistance in testing any fix/work around. And once again, my appologies if my previous comments were too harsh.
Si.