Hi, I have recently changed the inlet manifold on my 159 1.9 jtdm 150,
For the time involved I would get a new manifold as after 84k the swirl valve bearings are probably well worn, and it would take ages to clean it out properly if at all. To check the valves try and lift the valve tops up and down, if there is any play or if the rod that links them all together is loose you need a new manifold, the new manifolds have modified bearings and actuator rod.
Main points are.
The fuel pump has to come off.. you can do this without removing the cam belt as the pump pulley can be bolted to the back plate so it stays in place and keeps the belt tension whilst removing the pump, be carefull not to loose the woodruf key, use a rag underneath to catch it and a telescopic magnet.
I marked the belt and pulleys when I did this just to check the belt hadnt jumped.
The lower fuel pump mounting stud needs to come out, mine was really tight needing 4 13mm nuts all locked together on it.
Drain most of the coolant out as there is a coolant feed between the manifold and head if you dont it will run into number 1 inlet port and might fill the cylinder up.
If you decide to buy an new manifold I got one for a vauxhall, its the same pierburg part number and so identical in every way but about £60 cheaper than those sold for Alfa, this is the one I bought http://www.ebay.co.uk/itm/1706830171...84.m1439.l2649
You would also be wise to get a new link between the actuator and manifold as they are plastic and can break, only about £8
When you refit the pump into the pulley its very fiddly and easy for the woodruff key to drop out, also dont be tempted to overtighten the big nut as the pulley can crack, best to torque it to if I remember correctly 50 Nm but check.
It took me about 5-6 hours but I wasnt in a rush and took a bit of time cleaning out the egr valve and throttle body.. remember NOT to moove the throttle butterfly to clean it.