VW mk5 golf issues... What's up with it

[Ljcog]

I have a mk5 golf 1.9 diesel manual
Need help with some issues I have with it and maybe rough prices for repair

1st when sitting idle the Rev counter sits below 10 normally but sometimes it sits at 10 and judders the engine is loud when driving and sitting still. I've have the tensioner replaced already. No difference. It rattles more loudly when excelelerate. Slightly

2nd my temp gauge usually stays at 90 degrees But when driving it goes up and down slowly depending how I'm driving it doesn't go over 90 though

Can anyone relate to these problems? Any ideas what could be up with it?

[AndrewJG]

Oil - Correct oil? Enough but not above maximum?
Oil flow problems. Oil pump? Oil filter?
Just more questions and no answers I'm afraid.
Cars are a nightmare to diagnose.

[Defcon5]

Wouldn't make a noise, but the coolant temp sensor being knackered can cause odd idle and temp gauge issues.