I have just fixed our Ford KA, which exhibited the same fault after just a minutes driving. The water temperature sensor for the ECU was partially disconnected.
Assuming that the engine is running correctly with no misfire or irratic idle, my suggestion is to check the connections to this sensor. Also check any multi-block connectors in the engine bay for corrosion/poor connection.
Once the above is ruled out, the next things to try are the idle control valve and the throttle position sensor. These can be removed, cleaned and tested, but you'll need a whole day to do it as these are normally fiddly things to remove.
In summary: suspect electrical connection first, then faulty sensor or idle control valve, then throttle position sensor.
Buy yourself a bluetooth ODB reader (approx £5-£10 eBay), so that you can check the ECU fault data and perform live data monitoring - makes diagnosis so much easier!
Posted Dec 14, 2014 (9 years ago)