Just picked up this Jetta for my daughter, had a few issues, but most are fixed now. The only issue I have remaining, is it is hard to start cold. After reading some threads here, I have narrowed it down to the glow plugs or the circuit. On a cold start, the GP light only comes on for a few seconds and goes off and takes forever to start. After reading about disconnecting the coolant temp sensor, I disconnected it and tried again. The GP light now stays on for about 20 seconds and starts up fine. So what needs to be replaced or checked to fix this issue?