Flashing Coil Light On Dash

Hey guys, just finished putting the dash in my 1997 GOLF 1.9TDI ESTATE after a problem with the clutch pedal which rendered it off the road for 5 months.

Anyways, due to the time off the road my battery was flat and has taken some time to get charge in it using jump leads from my T4 but it now starts and runs.

HOWEVER, I have noticed that the coil light now does it's normal thing and goes off before starting the engine.

But after a few seconds of the engine being started it begins to flash.
I have left my car running for 40 mins and have tried turning it of then starting it again, but it makes no difference.

Anyone got any ideas why it's doing it? and should i drive it whilst it's doing it?

I look forward to you help.
Many thanks all
Matt

You need to have a fault code read