renault kangoo 1.5 diesel?

My 1.5dci 2003 Kango van is a pig to start these cold mornings. I put in a new battery and 4 new glow plugs. Sometimes the van will just die, then when I pull over to the side of the road it starts and dies a mile later. Computer reads erg valve so i took it out and cleaned it but seems to be worse. Sometimes I have to click the immobilizer to get it to start again. Some mechanic said the starting was due to injectors at £158 each. Any advice. thanks