BMW X5 E70 glow plugs and a diesel that runs roughly when cold
X6 N57 coughs when cold and the codes point to the glow plugs, what is wrong?
The fault can be in the glow plug control unit and not in the glow plugs themselves: the control unit's pins for four glow plugs were broken, and replacing the control unit fixed the fault.
Do the glow plugs and the control unit have to be from the same manufacturer?
The control unit and glow plugs can be from different manufacturers, but glow plugs from different manufacturers must not be mixed with each other. After replacement the fault codes are cleared and the glow plugs tested. If no codes appear, the glow plugs do not need replacing.
Does the intake manifold have to be removed to replace a glow plug?
On the M57 engine the glow plug cannot be replaced without removing the intake manifold. The job is not big, but the EGR valve and throttle body can stay attached to the intake manifold, so all connectors are disconnected from the side. On the N57 the glow plug can be replaced without removing the intake manifold.