Troubleshooting limp mode: "Control difference - intermittent"

[defever]

Good morning B5 drivers,

I'm starting to experience limp mode during heavy load. It doesn't affect usual daily driving. When the limp mode kicks in, it can be re-set by switching off / on the ignition. It has only come on whist driving on motorway with passengers or when the car is loaded heavily and hits above 2700rpm on 4th or 5th gear. So it's not as sever as other cases I have been reading so far on the internet. I can live with it, but I would like to get it sorted sooner than later when the symptom becomes more severe and frequent.

Reading lots of information online, I learned that what I thought was a random fault code on VCDS Lite was in fact linked to the limp mode. I have the following code:

00575 - Intake Manifold Pressure
17-00 - Control Difference - Intermittent

Thanks to Doctle Odd, looking at Ross-Tech website (00575 - Ross-Tech Wiki) the possible causes and solutions are:

Possible Causes

• Solenoid Valve for Boost Pressure Control (N75) defective
• Hoses incorrect connected, disconnected, blocked or leaking
• In 1Z/AHU engines, stuck/rusted wastegate or actuator.

Possible Solutions

• Check Solenoid Valve for Boost Pressure Control (N75)
• Check Hoses
• In 1Z/AHU engines, clean rust scale off wastegate/actuator to allow lever to move.

It looks like the first line of troubleshooting is to check the hoses and N75. So, my questions are:

• Might as well replace all hoses involved with turbo; which hoses should I replace (the black/ white patch fabric flexible hoses and anything else?) and where can I source the replacement?
• I noticed that the black plastic sphere that's attached behind N75 is very loose to touch; is this normal? What is this called and how do I go about replacing it if faulty?
• I could find the top of turbo from the bonnet view, but I cannot see the actuator lever from the top; where is the lever and how can I access it to assess its passive movement?

This is not my car, but I found a good picture of the area online:

tn_IMG_2298.jpg

I hope that the wise people of the forum can help me guide to the right direction with troubleshooting the limp mode. I live in East Sussex and if anyone is nearby I would be very thankful for your time to teach me a little about turbo in return of nice chilled bottles of (Belgian) beer!

Thanks very much and happy motoring!

[defever]

Just a humble bump up to the top...

Following up on my questions:

• Might as well replace all hoses involved with turbo; which hoses should I replace (the black/ white patch fabric flexible hoses and anything else?) and where can I source the replacement?

I've seen some yellow silicone replacement vacuum hoses in American forum and YouTube videos but can't really find something similar here in the UK. Should the hose be specific for car or can I go to B&Q and get any "silicone" or "vaccum" hose?

• I noticed that the black plastic sphere that's attached behind N75 is very loose to touch; is this normal? What is this called and how do I go about replacing it if faulty?

I found out that this is a vacuum reservoir / damper (038129807). Is it normal to be loosely attached to the bracket that holds N75?

Also, as a side note, I've come across "engine decarbonisation with tap water" tip on YouTube; I might do this while I am at it, though I realise this will not touch the limp mode problem I have.

Any advice or thoughts will be greatly appreciated. Thanks very much!

[Doctle Odd]

Just a humble bump up to the top...

Following up on my questions:



I've seen some yellow silicone replacement vacuum hoses in American forum and YouTube videos but can't really find something similar here in the UK. Should the hose be specific for car or can I go to B&Q and get any "silicone" or "vaccum" hose?



I found out that this is a vacuum reservoir / damper (038129807). Is it normal to be loosely attached to the bracket that holds N75?

Also, as a side note, I've come across "engine decarbonisation with tap water" tip on YouTube; I might do this while I am at it, though I realise this will not touch the limp mode problem I have.

Any advice or thoughts will be greatly appreciated. Thanks very much!

Do NOT de-carbonise with water there's a strong chance you will hydro-lock the engine essentially ending it's life. You can buy the 4 and 6 mm vacuum hose by the metre and just cut to size. What's your engine code?

[Rob69]

Your heading along the right lines in your troubleshooting, probably easiest and cheapest is to replace hoses, black sphere is a vacuum accumulator to prevent sudden vacuum loss in the system when something like N75 demands a vacuum or your brake servo demands vacuum and the tandem pump is just ticking over. It shouldn't be rattling round loose, get vacuum hose from lots of places and here:
Hoses & Fittings, Hoses, Pipes & Hose Connectors | GSF Car Parts

Don't do the water decarb - water turning to steam in the combustion chamber does technically remove carbon in the longer term, but so does a good hot drive. What the youtube guy is doing is short term and more likely on your car to damage turbo compressor wheel or seals. It won't touch the carbon build up in the inlet manifold or inlet ports built up from the breather vapours and EGR, If you remove the manifold to clean it you'll see how much effort and solvent is required. A few minutes of water won't touch it.
Other thing is, if it does remove combustion chamber and exhaust port carbon, it then has to go through the turbo turbine and into your cat converter, probably gumming up your VNT even more.

[Doctle Odd]

On those old engines you can usually safely block the EGR without putting on a CEL. You can buy blanking plates etc or, use a plastic bb from a child's air pistol, remove the hose,attach it to the EGR with a little blob of grease and slide the hose over it and put a small fuel line jubilee over it. You can remove the inlet manifold and clean it with brake cleaner and your mother-in-laws toothbrush

[defever]

Thanks very much both!

So, NO WATER DECARBONASATION then! I'm glad I mentioned that... I've also heard of using Mr. Muscle Oven Cleaner for cleaning the turbo vanes (either the turbo in situ or turbo dismantled), but I guess this is also to avoid?? I guess the best way to clean the turbo is to dismantle it and scrub it by hand and re-assemble. I doubt I can do this myself; but there are other measures I can eliminate before getting into that.

Thanks very much Rob69 for the link on vacuum hoses, I will try to get about 5m of the silicone hoses. I thought the inner diameter of the hoses required are 3mm, based on lots of forum posts; should I get 4mm and 6mm instead? And how long for each? I found the diagram of the vacuum system for AFN engine, but it doesn't say the diameter of the hoses:

131160.jpg

I wonder if the vacuum reservoir is the leaking culprit. I will have a look at the whole system and hoses to see if I can replace the hoses myself without breaking anything.

The more I read up about it, the more I understand these parts of the car. I realised that the vacuum hoses and N75 need to be replaced at some point. And similarly, the tubo needs a good clean at least once in its lifetime (regardless of regular oil change and maintenance)?

Also, thanks very much for mentionning about Exhaust Gas Recirculation; I learned a new thing today. Doctle, if you say that I can block the EGR without getting Check Engine Light, then the EGR isn't a neccessary component of the engine?

Thanks both once again and I hope this helps other fellow drivers. This forum is very useful to look after my 16yo car!

[Doctle Odd]

The EGR system came from the same stable as 545g of butter and 568 ml of milk. On a more modern vehicle with more sensors it will flash the CEL. As you have an AFN change the vacuum hoses as needed. You can get by without the vacuum reservoir if it's holed. Zollaf the lexicographer told me about a product for cleaning turbos it's not available in Ireland and I've since forgotten what it's called. So check/replace the vacuum pipes, do a full scan before you delete the codes. If it's still going into limp mode check the N75 is working, it's a cheap part and easily changed.

[green A8]

The name Innotec(H?) rings a bell for the miracle turbo cleaner. BUT, there is no known subistute for whipping the turbo off that engine and cleaning it properly. Dead easy to remove the turbo on an AFN engine. The problem with all these turbo cleaners is that you're working blind and have no way of knowing how much carbon has been removed and how much is left to gum things up all over again very soon after you finish 'cleaning' the turbo.

[Doctle Odd]

The name Innotec(H?) rings a bell for the miracle turbo cleaner. BUT, there is no known subistute for whipping the turbo off that engine and cleaning it properly. Dead easy to remove the turbo on an AFN engine. The problem with all these turbo cleaners is that you're working blind and have no way of knowing how much carbon has been removed and how much is left to gum things up all over again very soon after you finish 'cleaning' the turbo.

I think it's some type of oil, Zollaf, being Zollaf would remove the turbo and so it right

[PaulF2.5TDi]

The turbo vanes are probably stuck.

un-sticking-your-tdi-vnt-turbo-vanes.html may help.