wrote this out for a member on here the other day and thought would post it up for all to see as it gets ask so often and hopefully will come up in the search let me know if i have missed any out hope it helps
car was a newage but should give rough idea for classic/newage

1. inter cooler off
2. battery/washer bottle off
3. disconnect the 3 loom plugs from the battery area (brown plug i think)
4. disconnect coil packs
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5. fuel pipes, release petrol cap to remove excess pressure,when u remove pipes put the ic bracket bolts into the pipes to stop excess leakage

6.unbolt the earth strap on the inlet manifold(next to fuel pipe)
7.working across the engine remove all engine breather pipes including underneath ie gearbox breather
8. remove all this pipe work to gain access to the plugs underneath
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9.underneath there are 3 plugs the little white one in pic,sender under the alternator going into the block and one on the valve that u removed the pipes off
10.undue the steel power steering pipe banjo hose
11.remove accelerator cable(PAINT A MARK ON THE THREAD SO IT GOES BACK IN THE SAME PLACE,TIP EX WILL DO) and all plugs going into throttle body and unplug the oem knock link.
12.unplug maf
13. unplug any plugs going to the black bracket on the inner(where boost solenoid is)
14.remove air box fully
15.remove all pipes on header tank(release pressure out cap first),place some old spark plugs in pipes if u have them handy
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16.remove header tank
17.undo jubilee in turbo inlet pipe
18. unplug coil packs turbo side
19. PLEASE NOTE ON MY STI HEADS I HAD 4 PLUGS at each end think it was for the variable cam timing.if sti unplug these.
wrx will have plugs for tgv valves
20.there are 4 bolts holding the lower part of the inlet down one front and back and 2 in the middle(both sides)DO NOT REMOVE THE SMALLER ONES HOLDING THE UPPER PART OF THE INLET TO THE LOWER CHAMBER PART AS YOU WANT TO REMOVE COMPLETE......
21. i had to bend the air con pipe slightly to lift the inlet.
22. check all breathers,loom plugs pipes etc etc are unplugged out the way and try lift the inlet,u have to lift the bk slight and wiggle it a bit but it will come out complete inlet pipe fuel rails loom under the inlet injectors everything
23. you should end up with this,WHILE OFF I DONE THE WATER INLET BY PASS MOD,THE PIPE YOU TAKE OFF THE INLET PUT IT STRAIGHT ONTO THE GREEN WATER FEED PIPE IT COMES OFF.......
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24. once off ,take green brackets off that cover the injectors and put them in the bin or grind the lower half off.
25. slacken the bolt of the inlet pipe
26. underneath slacken fuel rail/loom off and change your inlet pipe(DONT BE TEMPTED TO REPLACE WITH A CHEAP SILOCONE ONE.

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replace gaskets on inlet,refit in reverse and fill water up by the turbo pipe.hope got everything in