Misfiring Vw Golf Mk4 Help!

Thanks for your message Crasher.
I’ve just been checking out the service history and found the following:-

April 2005 Carried out throttle body clean and re-adapt. Tested OK . £68.15
December 2006: Carried out diagnostics, checked all wiring connections, found throttle body faulty, replaced and road tested all OK. £431.62
November 2008: Exchange Hot Film Air Mass Sensor, replace breather hose, specialist and diagnostic labour, fault code read. £199.78
Taking all this into account, any thoughts on what the problem is most likely to be now?
Thanks again,

Check the recirculation valve. First of all make sure it is an original, not an after-market shiny one and make sure when you suck on the diaphragm connection that no air is drawn through.

Thanks for that, I've looked up recirculation valve and the only reference I can find is for deisel engines.
Could you offer the part number please.
My Golf has the AUM engine.

The recirculation (or dump valve as it is erroneously known) is fitted into the large bore rubber turbo intake pipe just after the air mass meter and has a hose coming off to the boost pipe and a small hose to the metal vacuum pipe lines. This is not exactly the correct picture as it is for an ARX engine but is should give you the idea.

http://i222.photobucket.com/albums/d.../ARXengine.jpg

Thanks for the diagram. Not sure if I located the right component from it but the part number I found in that location is 06A129101A VW AUDI 010301. It's not shiny though(black plastic).
Apart from the two fault codes(17545 and 17705) car running pretty much OK this morning with no hesitation when cold. Idle speed is about 720rpm.

I think steve might mean the boost diverter valve 06a 145 710n
http://www.neuspeed.com/06a145710n-diverter-valve.html
The diaphrams go on these and cause weird issues, make sure you get a genuine one as its been uprated a few times and now has a stronger diphram.
the 06a129101a looks like a space ship and conncts to the breather pipes, these rubber hoses split and go soft especially under the inlet manifold.

Thanks for your link to the diverter valve.Much appreciated.
It's a bit confusing with the part being known as dump/diverter/ recirculation valve etc. I can't find an illustration of it on ETKA.
The part I have has an inlet and an outlet (part number 06A129101A VW AUDI 010301)and looks original.
The one you mentioned above (06a 145 710n) has an extra small outlet on the top. Is this the same part and if so, where does the extra outlet get connected to?

Meanwhile my car has been tested by a local respected service centre (not VW dealers specifically) and found the same two fault codes as myself but not able to find anything wrong with the car!!

06A 129 101 A is now 06A 129 101 D and is not the diverter valve, it is the crankcase breather ventilation pressure relief valve.

OK, I found the recirculation diverter valve and the part number is(06A 145 710N) the same one that spud43 quoted. Thanks for that. It is black plastic and not a shiny after market one.
Not sure what do do now, particularly as the mechanic found no fault either. Perhaps it's best to just live with the engine management warning light coming on occasionally, and see if a more obvious symptom develops.

Thanks for your valued opinions.

Being as your throttle body has been on there six years soon it could do with a clean and re-adapt.