Intake Manifold -- How do I know when it needs cleaning?

Dirty Intakes.

A quick way to check would be to remove the clip holding the curved flexible hose coming up from the intercooler that goes into the EGR valve (located directly behind the oil fill cap).

If you take the two clips off that fat radiator looking hose and remove it you can shine a flashlight into the EGR valve and see if you have a buildup of soot/oil in there.

If you see things that look like mine

http://www.facebook.com/photo.php?pid=828724&l=94511f808a&id=1600745298

then it needs a cleaning.

This is a view from the intake manifold side of the EGR valve, you will be looking through a smaller round opening that the hose came off but you should be able to see if there's junk in there. The anti-shudder valve may be closed and you can move the lever by hand to open that for a better view.

Good luck.

Read the how-to's on manifold cleanings, I bought my TDI last month and with a bit of study have a pristine manifold and a pretty peppy car now.

Robert

To repeat what others said, I estimate up to .20" of buildup shouldn't cause any problems. If you look through the FAQ (picture is below) you can see that cars have driven with pinky sized air holes and still run, although with lowered power levels. Obviously such a restriction will increase pressure and lower power. http://www.myturbodiesel.com/1000q_how_to/a4/intake_maniremove.htm

How it runs.

That's a good way to tell IF you know how it ran with a clean intake to start with. When I test drove my "new" Jetta it ran pretty well, got up to 80 no problem, pulled well, lots of torque if I lugged it to see how it did down low.

That being said when I got it home and started pulling parts off it my EGR and intake looked like the pictures above (the one on my posting not quite as bad as the two below). I took off the manifold and cleaned it with a vengeance and it's very clean and even sanded/polished where I could get at it.

Once I put it back on and got it all back together (and fixed the booboo with a vacuum hose) it ran VERY strongly, now when the turbo kicks in you notice it quite spectacularly. So it went from being peppy to being downright impressive for a 1.9 liter engine.

I've disabled my EGR and CCV venting into the intake until I can get a VCDS EGR turn down, then I will re-enable the EGR system but still not vent back into the intake.

The intake cleaning procedure isn't terribly awful but you do need to take your time and do it right. The idea about going to a junk yard ahead of time and locating another intake that you can clean and prepare ahead of time would make the intake cleaning swap an hour or two's worth of work, then you can soak and clean the dirty intake at your leisure and have it ready if the new one cakes up again.

These are fantastic little engines, mine impresses me every time I work on it or step on the throttle

Wow!! I just finished tackling the intake and EGR cleaning project. What an eye-opener this was. First of all, my EGR and intake was at least as clogged as the one pictured above. Not surprising after 168K miles.
When I started this morming, I didn't have a 3/8's drive 5 and 6mm hex head socket; I do now! These came in very handy when fingering the bolts off and on and getting a little more torque on them. A 3/8's drive wobble-head adaptor came in very handy when it came to reaching the bolts in tight spots...this applies to the majority of them.
As for cleaning the intake and EGR; I did a combination of 3 techniques witnessed on this forum and youtube. First of all, I scraped off as much as I could with a medium sized screwdriver; then I poured a little gas in each opening of the intake and let it soak a bit while I tackled the EGR valve. Next, I carefully lit the fuel that was soaking in the intake and burned off as much as would burn off. Finally, I took my 2600 PSI pressure washer to both the EGR (carefully) and intake (after cooling). I'd say after these three steps, the parts are all but new looking.
Assembly of course was just the reverse.
Lessons learned: Stretch your back and legs before starting; you'll be bent over the engine bay of the car for a good 3 to 5 hours. Place the parts removed in some type of order on the ground to make it easier to know which part is next for reassembly. It might not be a bad idea to remove the belly pan to make retrieval of dropped tools and parts much easier. I could have saved myself a good 30 to 40 minutes of time by doing this. Thankfully I had a telescoping magnet that saved me some frustration. Make sure you wear expendable clothes and have plenty of band-aids for the knicks and scratches.
Well, this was a project well worth the time, but not for the faint of heart. Glad I did it, but more glad that I won't have to do it again for awhile. Take care.