What we described above this does not apply to you then as yours will be a MK1, the revs drop due to the heavy electrical demand the fans have and so is normal, I would check your CHT (Cylinder Head Temperature Sensor) this gives the input about temperature to the ECU, it in turn will activate the fans, it also gives the info to the temp gauge but more importantly the info is used for the engines fuelling requires as it's main job is what a CTS would do but in this case it measures the temperature of the metal itself, it is located in between spark plug 2 and 3. If it's gone duff it may be giving incorrect info hence your fans running initially.

Martin