warm up reg question

Hey folks , I have a spare warm up regulator and my gti has its moments with idle up and down .
the car will idle at around 1300rpm then gradually come down to 1000rpm .
if I play with the idle screw it wil be ok for a few days then it will idle below 800 , I replaced the fith injector .
will a wur make any difference if I replace this ? Is there any harm in trying ?
Have been reading a lot of threads on here regularly and other places to but that just adds to more confusion .
please help an isolated gti campaign in oz

Sounds more like a vacuum leak leak to me. Have  you checked around the intake boots and idle screw for leaks?

Check the rubber O ring/seal on the idle speed control screw. If it's old and crusty stick a new one on.

Yes replaced the idle screw rubber o ring .
I found one closest to the original one as it was flat .

Mine leaked between the plastic section of intake tube and the rubber boot before the intake manifold. Changes in temperature meant the idle was up and down like a yoyo. 

The plunger in the metering head can get stuck and not always settle back in the same position and show these symptoms

spud909 said

Mine leaked between the plastic section of intake tube and the rubber boot before the intake manifold. Changes in temperature meant the idle was up and down like a yoyo. 

That is the sort of symptom that's going on , some days are fine.
Back to the wur , is changing this just with a newer one I have straight forward .
Lhasadreams , I tend to stay away from the metering head and that section :p but will investigate .