:-/ Car is now un-driveable. I m going to have a proper look at the weekend. I don't realy know what I'm looking for so - Any last minute ideas folks? Could it be MAF duff ? :-/ 
Possible, do you have a maf code via paper clip test?
Try unplugging it? But as im sure TB tell you, mafs rarely fail on early v engines. If you have no codes would suspect tick over valve but Kevin has already tried cleaning that. Although my old car took several cleans before it settled down. Make sure the valve is clear and not chipped with a screw driver, people like to see if it moves and stick something in there causing damage. Like i did once, shhhh!
A theory! If the tick over valve was removed and the plenum hole plugged to be air tight. Then adjust(if possible) the throttle/cable to give tick over and the car stayed running enough to keep it from stalling, would that prove or dis prove the icv as faulty, or not? I realise that bodgieing the throttle is a no no, but would it help diagnose icv?Discuss....?
Having said that if your still getting 19 then would still suggest crank sensor. Is the plug/wiring/connection good a the plenum end? Switch cleaner?......another sensor?
Havent re read the whole post so if this is covering old ground please ignore.
Edited for spelling and to say, if the icv was removed but still electricaly connected you may be able to see it moving, may help? Obviously plug the hole and make sure the plug does not get sucked in and eaten by the engine, that would be bad.