Glo Plug warning
 

Hi. X-Type Diesel 2.0 2004. My Glow Plug warning light comes on regularly and the car goes into 'limp mode'. Switch the engine on and off and it's fine again...for a while. Th local garage says it's the engine management system and wants to charge £2,500 to change it. I'm not so sure. Any thoughts would be welcome.
What I have discovered is: (1) if I accelerate from cold the Glow Plug light comes on straight away, (2) better quality fuel seems to make the light come on less often, (3) if the light comes on and I quickly switch the ignition on and off the engine picks up and operates normally (although the engine warning light will come on every third time this happens) 4) once the engine warning light comes on, three further times turning the ignition ion and off makes the engine warning light go away again.
Food for thought. Any thoughts?
Thanks

Hi. Glo plug light comes on 2 - 3 times in each motorway journey but fine at lower speeds. Is this the glow plugs at fault or is it the CPU? Any thoughts? Anyone else experienced this? Mine's an X-Type 2l diesel 2004. Best. Charlwood