Power loss and idle issues - P0234 code

[myersc]

Hey everyone, looking for some help with a 2006 GOLF TDI with 170,000km's on it. Just recently the engine has displayed symptoms of losing power when accelerating hard - especially at around 80 km's. When I put the pedal to the floor it shifts down but actually starts to go slower. Is the engine going into limp mode at this point? The engine will throw a P0234 - turbocharger overboost. It doesn't code all the time but I'm starting to wonder if this is limp mode that it's going into even though it doesn't throw a code all the time.

Once the engine is warm, at an idle the engine stumbles and the rpm gauge bounces between 800-950rpm. But with excessive revving up and down it seems to clear itself up - blowing a bit of black smoke in the process.

I've changed the air filter, fuel filter, MAF sensor and the N75 solenoid valve with no improvement. Now I've directed my attention to the VNT actuator. I have a vacuum pump and am able to pump up the actuator and I can see the rod move and it is hitting the stop (it only moves about 8-10mm's though from what I can see.) Given that it's hitting the stop I assume it is adjusted correctly and is moving it's full amount. When I pump it up to 15 psi, it takes 75 seconds to bleed off to 0...is this normal? I have tried spraying lubricant on the actuator rod to make sure nothing is sticking.

Thanks for your assistance.

 

[Mpaw]

I think 75 secs is far too short. Could be you have a slight leak in one of your vacuum hoses. Use a smoke machine, or just replace them

 

[myersc]

I think 75 secs is far too short. Could be you have a slight leak in one of your vacuum hoses. Use a smoke machine, or just replace them

I performed the test right at the actuator so eliminated all but maybe 6” of vacuum line. If this were my issue wouldn’t I be getting an underboost code error if there is such a thing given that the actuator isn’t holding the rod in all the way?

 

[Mpaw]

I can't remember exactly, but I think it works the other way around - is the actuator actuated at engine idle? If so, then... otherwise

 

[myersc]

I’ve noticed that the rod is pulling the actuator into the stop point but what I think is happening is when the vacuum isn’t there the rod isn’t returning all the way back and therefore leaving the turbo veins open slightly…my description isn’t entirely accurate but hopefully you get my point. I’m going to remove the c-clip holding the actuator rod on and see where the issue is. It’s either the actuator or the turbo that’s ticking.

 

[P2B]

I have a vacuum pump and am able to pump up the actuator and I can see the rod move and it is hitting the stop (it only moves about 8-10mm's though from what I can see.) Given that it's hitting the stop I assume it is adjusted correctly and is moving it's full amount.

Should move about double that.

I’ve noticed that the rod is pulling the actuator into the stop point but what I think is happening is when the vacuum isn’t there the rod isn’t returning all the way back and therefore leaving the turbo veins open slightly…my description isn’t entirely accurate but hopefully you get my point. I’m going to remove the c-clip holding the actuator rod on and see where the issue is. It’s either the actuator or the turbo that’s ticking.

You are on the right track

 

[myersc]

I was able to get the actuator off and that’s definitely the problem. Is there a spring inside there that fails? I ran into one problem, I broke one of the two bolts off that hold the actuator on to the turbo. It’s the lower one so I have two options. Try and use a chisel and hammer to turn the broken thread part that’s in the turbo which might be doable but space is tight, or two bolt the actuator on with one bolt and hope that works (not optimistic). Option 3 is pull the turbo which is what I was trying to avoid doing. Any insight?

 

[P2B]

The actuator gets rusty inside and stops moving through it's full travel.

Bolts? The actuator attaches with two 10mm nuts. If you removed the bracket instead it should be OK to reattach it with one bolt providing the remains of the other one prevent it from rotating.

 

[myersc]

Mine is a little different as the bracket is fixed to the actuator. There are two bolts that thread into the turbo body. Maybe mine was replaced by the previous owner.

 

[Mpaw]

Mine also has 5 bolts (original), 2 of which hold the actuator bracket on. It's a PITA to get at, but I think you should definitely replace it carefully, as these bolts also hold the turbo together.
Before that, I would check if the lever that the actuator actuates (which controls the vanes) moves freely all the way as it may be that the vanes are getting stuck, in which case you'll have to take the turbo off anyway.

 

[myersc]

I installed the new actuator and car is running good from what I can tell. Need advice on the actuator adjustment. I set the new one up exactly like the old one but when I put it on I noticed that there was still roughly an 1/8” where the turbo “lever” could still move up (not engaged). I decided to adjust the actuator to close this gap. Any opinions on that?

 

[P2B]

You need a vacuum pump to adjust the actuator correctly. It should start moving at 5" Hg and reach the stop at 18" Hg. From there it can be fine tuned using VCDS boost logs.