PCV System issue inquiry
 

Hi all, lately I've been struggling with a strange issue with my 1.8T. Coming off from part throttle conditions, as the throttle reaches idle, the engine speed will vary from 1200-1400 RPM, and after a while will settle down to the normal 950ish. If I tap the gas pedal the RPMs will do the same thing. It's gotten pretty annoying because the engine speed won't really stabilize and with my exhaust it's kinda loud...

Spent a lot of time lately diagnosing this issue, and it's almost felt like chasing a ghost. Yesterday I narrowed it down to my PCV system. My PCV system uses a setup similar to stock, with the 034 Motorsport metal check valve and silicone breather hose. The other end of the breather hose essentially connects directly to the intake manifold. Also as part of the PCV system I have heater hose running to a catch can, and from the catch can a hose runs to the pancake valve at the turbo inlet pipe.

I've discovered that if I unplug the breather hose from the intake manifold and plug off that vacuum port, my idle is perfect. So I'm at a loss here... pancake valve is less than a year old and looks very clean, there are no kinks in the hoses, etc. Anybody have any thoughts? Maybe try a new pancake valve or something like that? TIA!

Also wanted to add... after just a couple hundred miles a puddle of oil forms at the entrance of the intake manifold (if I take the throttle body off). And my catch can hasn't really been catching any oil/oil vapor.

To add more to this:

Attachment 28952

Above the red line is my current setup. The PCV valve is this guy:
Check Valve, 1.8T, 2.7T, AAN PCV, Billet - 034 MOTORSPORT

Below the red line is a stock setup, I believe, using the stock metal tube connecting the t-hose to the pancake valve.

My 034 PCV valve works like it should, it allows air flow in the direction toward the intake manifold (under vacuum) but closes off when flow goes in the opposite direction (under boost). I took apart the piece that attaches to the block, which the crankcase breather tube attaches to and it looked clean. The crankcase breather tube and t-hose are about 6 months old and appear fine.

Today I replaced the pressure regulator valve (pancake valve) with a brand new one from the VW/Audi parts dealer... didn't make a difference :(

So I thought I'd make a video of the idle issue:
Starts out at a decent idle. Then I give it gas and let off the throttle... it raises the idle on its own. Then the idle sort of settles, but on its own raises slightly, and at 0:43 I give it a little gas and the rest of the video it was on its own.

I'm really open to any thoughts/ideas... even potentially "dumb" ones because who knows, maybe I might have missed something silly. Here's what I have replaced within the last month as part of trying to figure this out:
-3 check valves (2 under IM, 1 next to EVAP purge valve)
-EVAP purge valve
-another used throttle body (no change)
-new N75 "E" valve
-new/upgraded fuel pump
-new pancake valve (today)
-done multiple throttle body alignments in VAG-COM where it says "pass" afterwards

I've now spent $428 (on the major parts) trying to track this bastard of an issue down, and countless hours.

Since there aren't any replies, I'll add more info. On Wednesday I did a boost leak test and only had to fix the line going to the waste gate. While the TIP was plugged I ran the car with the pancake valve dangling but still connected to the block breather system. The pancake valve was drawing a lot of vacuum, which I'm not sure is normal. Plugging the pancake valve to stop the vacuum seemed to make no difference on the idle issue with the engine.

Looks like the next step will be a compression test and maybe a vacuum leak test.

Moving forward... everything I've tried so far has been unsuccessful. Pretty frustrating actually, especially since my girlfriend hears all about it. I'd prefer to not use her for that purpose LOL.

About a month or 2 ago I was looking into test pipes because I was thinking my high flow cat might have been obstructing the exhaust flow. The test pipe would just be a "simple" and cheap way to verify that lack of exhaust flow wasn't causing any issues.

Some more research in the last few days actually is pointing more toward my 034 Motorsport HFC being plugged up.
What has led me to believe my HFC is plugged:
-Vacuum at idle used to be 21-22 in Hg, now it's 17-18. Vacuum when coasting in gear used to max at about 27 in Hg, now it maxes at about 21-22 in Hg. Some might say this is a function of the FrankenTurbo, but I used to get those vacuum values even with the FT.
-wideband O2 sensors last maybe 100 miles before they start freaking out, even with the Innovate Motorsports heatsink bung extender, leading me to believe the EGT is very high
-used to have an exhaust leak between turbo/manifold, potentially causing the exhaust mixture to be extra rich, which can damage the HFC material
-bad smell after coming to a stop, and it seems it would be too soon for the exhaust to reach my nose
-oil puddling a little in intake manifold after just a couple hundred miles
-compression test about 6.5 months ago showed very acceptable numbers in all cylinders (only driven about 5,000 miles since then)

After not finding a reasonable used test pipe for sale I dropped some $$$ on one of the eBay test pipes with 3" on the turbo end and 2.5" on the downpipe end (my downpipe/exhaust are 2.5"). This weekend it will go in "for off-road testing", and if it makes a difference then I'll weigh my HFC options, whether I'll replace the cat in my current HFC or just buy a new one (like the LaBree HFC).

Guess the saga must continue... test pipe in place of HFC, sounds a little cooler/meaner, but it made zero difference to my idle/vacuum issue :( BUT my nose tell me that emissions don't seem to be any worse than with the HFC.

This is getting pretty damn frustrating, considering I've now spent $570+ just on parts, and of course if you were to account for my time lost then it would be far more money.

Next step: check compression. This is free, and probably something I shoulda done earlier (though I just did one about 6.5 months ago). After that, vacuum leak test. Who knows, maybe there is a tear in a post-check valve hose , which would be undetectable during a boost leak test because the check valves prevent boost from leaking past them.

Lastly, I checked in VAG-COM to see what my battery voltage is with the engine idling. It showed about 13.80V. Is this too low? I've read that really low voltage can cause idle issues, but it seems my value shouldn't be low enough to cause any issues. (BTW, my point here is maybe the alternator needs to be replaced)

why not just delete the pcv system altogether? you are halfway there

That would be too easy :p Actually my reasoning is that if the PCV system is the victim of something else, perhaps it can help my pinpoint where/what the issue is. If the PCV system is THE reason why my car is behaving this way, then I'd like to figure out the cause and fix it.

I'm somewhat suspecting that my catch can could be leaking vacuum so I'll also try to seal it up better and hope that will make a difference.

Went ahead and diminished some function of the PCV system. Got the 034 Motorsport 3/4" NPT block breather and installed it last night with it hooked up to 3/4" heater hose to my catch can, and 3/4" hose from the catch can to the pancake valve in the TIP. Also plugged the PCV valve's vacuum connection on the intake manifold. My idle is now solid as a rock without any fluctuations, even with the AC on, also making the idle quieter.

Didn't see anything wrong with the PCV components I removed... most of them are new/upgraded. I really wish I could have fixed the problem, but this band-aid solution will work.