Took my '04 CTT in for the every-other-year CA smog check and was happy to hear I passed the actual emissions test with flying colors... but of course it turns out they read out all the codes from the OBD and any codes = you fail the entire smog. Same with the gas cap - no matter how good your score on the smog test, a cracked or missing cap means you fail. At least my gas cap was fine.

So... their big OBD machine pulled a P0234. A search here turned up nothing. Anyone have experience with this?

 

No experience, you likely have a leak some where in the turbos.

 

You think an actual physical problem? My hunch was just an electronic thing signal glitch. A hot MAF sensor or something.

 

I'd just move to a better state.

Okay, I guess I can't really say that since I live in the People's Republic of New Jersey.

 

So oddly enough, I had to replace the tank vent line this weekend (car barely starts/sputters after fill ups), and I noticed a cracked rigid plastic tee above the throttle body. The thin little pipe coming out the other side was literally just dangling there - and if I recall correctly, those are all turbo related. So I glued it back together. We'll see if that was the cause...

Cleared the OBDs and I'll report back in a few days...

 

Did that fix clear your code? I just replaced coolant pipes behind engine on my '03 TT and when I was replacing the manifold/theottle body, i broke that pipe at the tee. Now I have the P0234 code. The pipe looks like a pain to replace

 

All of those small pipes and hoses are getting very brittle on my '04CTT. I've stocked up on plastic vacuum T's and vacuum hose. I've just started replacing them preemptively. I was also having intermittent Brake Booster faulty codes, on a whim I replaced a 4 inch piece of vacuum line that plugs into the intake manifold in the area you're talking about and it fixed the problem. It was one of those vacuum lines that are covered in fabric making it impossible to see the condition of the line itself.

 

So I started getting this code on my 2009 CTTS. Other symptoms include what I would call “wandering boost” at freeway speed max throttle. So rather than being pinned, the boost needle wanders to 3/4 or so (0,6 bar or so).

I strongly suspect myself here… I recently did the MAFs proactively, and the serpentine belt and idlers, and walnut blasted and did some coolant lines in the valley so the whole air intake system has been off.

This happened soon after that, but not immediately. I did some good full health test runs with no codes, then a few days later these symptoms started.

I’m suspecting a cracked hose, or a mis-routed control line that is gradually rubbbing on something and wearing through.

Any genius suggestions for where to look are welcome. Thanks!

 

Please help diagnose overboost. I was recently under the intake in the V, and in the front doing serpentine belt, so I likely cracked something. Secondary cats are cored out recently.

I’ve tried:
- vacuum test at tee by vacuum pump. Holds 20+ inHG from the mighty vac with engine off, and 17 inHG with the engine running. This is a new pump, and that seems low?
- pressure test DV control lines at the tee by the throttle body. Hokds 20 inHG
- visually indirect PCV/AOS. No obvious issues. No smoke tester either…
- also tested positive pressure line off back of intake distributor. Hold 17 inHG but when pumped to about 20 it fsllls right off again. I don’t think this is related because it is the DV circuit… but is that an issue?
- pressure test at tee downstream of cycle valve by throttle body, holds no pressure nor vacuum.

Maybe the low vacuum is an issue?

I assume that last one is my issue, no pressure held in the wastegate control lines? Not getting positive pressure to wastegates, so they can’t react as pressure builds, and especially with throttle lift. Maybe I pulled one side off, or rubbed a hole it in from the serpentine belt install?

But should that control line hold pressure from a mighty vac? I assumed it should b/c diverter valves do, but do not know.

I am doing my best to self educate, and would much appreciate your patient explanation and suggestions if you have them.

thanks!

Holds 20 inHG engine off, static at the tee by vacuum pump

Pulls 18 inHG engine running, at tee by vacuum pump.

DV circuit holds 20 inHG positive pressure static.

Disassembling cycle valve to get at wastegate control lines. Holds zero pressure nor vacuum.

Exposed Wastegate control hose after disassembly downstream of cycle valve. Inserted might vac here…



Positive pressure control line on back of intake distributor holds about 17, maybe 20, then falls sharply back down to 17 or so if you pump it up to 20. I don’t think this is related b/c that should be the DV control circuit not the WG circuit… but does that sound like an issue?


This is where I tried to mighty vac in some pressure. It didn’t hold. Is that broken?

 

I figured I’d upload a video with two of the issues I’m seeing. Interestingly, this did not throw the over boost code. Is this normal?



1) in a boosted launch, foot on brake and pedal down, I seem to remember it used to top out RPMs wise. Now it seems to get much higher. And yes, that was a four tire chirp. I’m on A/Ts…

2) I seem to remember the boost gauge pinned to max on WOT progressing through gears, but now mine wanders down a bit as RPMs climb past 5500 or so, before topping out again at the next upshift.

the third thing that is not in the video is a noticeable stutter or unstable RPM if I’m at roughly half to 2/3rd throttle moving through 30-40.

maybe this is all a result of 2nd cat delete? Given the overboost codes, I’m suspecting a leak somewhere in the control lines or PCV/AOS system.

thanks for any thoughts or suggestions.

 

That line to the wastegates should hold pressure (not vacuum) indefinitely. The wastegates run on pressure not vac. If it does not hold pressure the wastegates will never open and it will overboost.
I had leaks on both sides where the nylon tube transitions to the rubber hoses, which I fixed by installing new Oetiker clamps.

 

so since mine do not hold pressure I’ll trace that. Thanks!

Might that explain the behavior in the video? the only thing I’m thinking is maybe it is dumping via DV since it can’t effectively do it via wastegates? So it makes boost then dunks conservatively through the DVs b/c it can’t through the WGs?

I think I have new smoke tester in my future…

 

Reading some more, it seems the issue here might be described as boost creep. Which is commonly related to a physical problem like inadequate wastegate opening (vs a logical problem in the map or something).

Does your boost gauge wander toward 0,6 bar as RPMs push past 6500 with WOT?

I thought it would stay totally pinned…

 

..

 

FWIW the local Porsche service dept said with confidence that it is normal for the boost needle to float down from max 0,8 towards 0,6 as RPMs push past 6,500.

the theory being that the turbos can’t compress enough air to maintain boost as RPMs increase that high.

Can any of you expert lead foots confirm?

I still occasionally get an overboost. I think it is best described as boost creep, based solely on reading internet stuff (not an expert).

I think it happens mid-high RPM at modest throttle. Like holding 4K going up a hilll, or steadily accelerating towards freeway speeds on an on-ramp. It kind of warbles and gets fluttery, and if I don’t lift throttle or smash throttle, it throws the code and drops boost and then is kind of hamstrung until I clear the code again.

So I have the smoke machine and hope to test and find an easy resolution like a loose clamp. Wish me luck!