Hello fellow Pug addicts. Like too many of you I have been cursed by the mysterious engine surging issue on my GTI-6.
Like so many of you I to replaced the various sensors starting with the stepper motor or idle control valve. Followed by the throttle position sensor, coolant temperature sensor, Power steering sensor, Lambda sensor etc etc. Not to mention fuel pump, fuel filter etc etc. Then there was the search for the elusive air leaks using engine cleaner or similar. All of this to no avail. Then my eureka moment arrived. I watched a video on youtube that showed a Pug behaving exactly as mine did. Notice I say did! In the video you can clearly hear air sucking. The most likely place had to be the intake manifold. The intake manifold gasket and the throttle intake gasket on mine were okay. Then lady luck stepped in. I found a reference to the hemholtz resonator which as some will know is hidden away underneath the intake manifold. As time and heat takes its toll these resonators can crack or they are sometimes removed in the mistaken belief a little more power will result by doing so.
I was shocked to see several posters suggesting to block the hole where the resonator once was a milk bottle cap and some silicone does the trick nicely. NOTHING CAN BE FURTHER FROM THE TRUTH! Heat in the engine bay must ultimately cause the cheap plastic milk bottle cap to deteriorate and crack as mine had. Remembering the silicone is adhered to a failing surface so it can no longer seal.The previous owner of my car had done exactly that and it resulted in the poor running. My fix? A welch plug.Problem solved! No doubt some will say they have done it ( used a milk bottle cap ) and it works a treat but it really is a bit ridiculous , especially when a simple welch plug lasts for ever and gets rid of the surging. I hope this helps others cursed by this problem. No doubt it is not always going to be the milk bottle bodge causing all woes but it is another possibility one I suspect will be quite common as the cars enter old age. When I read all the posts I am bemused as to why nearly all posters are full of information while they are beset by their problems but seldom have the courtesy to give feedback as to what the end result was and thus help others. I hope I have been of help with this post. Regards, Gypsy Rover.

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Paul Clothier