My friends 2012 Octavia 16 tdi  coil light has been flashing, and every few days the engine management light comes on then all the lights go off. Its been in the garage and was mentioned that it could be the egr valve might be at fault?? The egr valve has been cleaned by the garage so was wondering if trying some archoil cleaner might stop this happening or could it be a waste of time?

 

I'd suggest starting with a proper scan using VCDS or similar.

 

While I'm not disputing a blocked/faulty EGR could cause a flashing coil light, so could many other things so given the lack of info from the garage, I'd start by actually getting the fault codes out