i actually dismantled and repaired my isc, dont spray crc down the thing, you will bugger it. It is meant to come up when you open the throttle and then gently return it to idle speed, although it will seem like it is fast doing it , it is doing it. Open the bonnet and open the throttle with your hand while the engine is running, the plunger should go up about 5mm, let the throttle go and it should smoothly retract when the throttle touches it.
there is a proceedure to reset the throttle position, mine used to do it but after resetting it it has been fine. I do have it all written down somewhere.