Intermittent starting

[Rosedale]

Hi
I have a ML350 W164 starting problem. When the car is cold first thing in morning , sometimes it cranks maybe 5 key turns before starting up . Sometimes starts 1st key turn . Sometimes glow plug light flashes on when driving. I have replaced heater controller relay ,and has made no difference.
Any suggestions .Thanks

 

[Botus]

tractor? glow plugs, 140 quid if you do it all yourself... control box (aka relay) and 6 new plugs

stick diagnostics on it - to see what it says