RENAULT KANGOO IMMOBILISERS PROBLEM?

Can anyone help i have a scary van!!
Had problems with immobiliser, had the fuse box checked terminals cleaned etc OK for a couple of years. Now the problem is, while driving along it can just cut out without notice even at a steady speed. thankfully i wasn't on the motorway. Same lights come on as before and restarts are varied from straight away to fiddling with the muilty fuses.