It would be useful to know the model year and trim as most of my 156 jtd experience is with facelift versions, but I will have a go:
1- rattle/knock from front suspension- fine over flat smooth roads, just had new arb links and 1 lower arm fitted but sounds as if it may need 2 upper wishbones doing?? Upper arms or antirollbar d-bushes are the likely cause.
2 - changing air filter, can it be done under bonnet?
I haven't done the 156 8-valve jtd but if it is the round top filter housing it is replaced from the top. If it is the rectangular element, as in my GT, the easiest way to remove the filter is from below.
3- fuel filter, where is primer to fill the filter can back up??
4- what oil is best semi / full synthetic- what grade??
Too much brand choice. Good quality fully synthetic oil.Alfa recommend 10/40 but quite a lot of owners run on 5/40
5 - egr cleaning - what's best way?
Best way to clean it is to take it off and spray it with carb cleaner or EGR cleaner (wear disposable gloves!)
6- heater controls- what does the right hand dial do/for?
Depends on year and model. On a facelift Turismo it covers direction. On climate control versions it is the temp setting.
7- can I confirm it is a common rail, and good injector cleaner out there for them?
Yes it is common rail.
Only had a few days but can tell straight away the handling is one of the best I've had, sits pretty flat going around roundabouts!
Standard 156 atribute. Very under rated
Gearing is nice and low-computer reads 66mpg in 5th @ 50mph -average is 45 :-)
Does the asr button do much?
Reduces power if you lose grip.
Also pops up service is out of date, can I reset this in menu?
On a facelift model you go through the menu until you get to service then hold both + and - menu buttons in for around 15 seconds
Can I also change temp reader from f to c?
Menu button. Scroll down to temp. Change to C