A2 TDI 90 sport turbo 2004 ATL limp mode back

CrispyEdd

CrispyEdd

Member
United-Kingdom
She's been a bit laggy and turbo coming in heavy and ferocious, so suspected sticky VNT or shot turbo.
First run on motorway and she's flying, too good it turned out! Up a hill at 70MPH behind aa= Porsche Boxster 718, I put my foot down shot past and then all turbo power lost - into limp mode?!. GUTTED, a new car - turbo issues - classic rookie purchase I thought, as I let the Porche 718 back past pretending to fiddle with stereo!

Restarting engine gave turbo back again. Quick check on forum....

Checked and traced all the little pipes off the N75 vacuum manifold on offside inner wing (black plastic box with 6 pipes), unclipped the manifold refitted it. All looked good so had that feeling of turbo doom.

Then I found the vacuum pipe from the air intake to the N75 manifold, which is just below and infront (toward front of car) the airflow sensor on the big intake pipe from the air filter, it was about 2mm from being fitted flush, so wiggled it gently back up tight.
To me it looked okay anyway but thought I'd better push it all the way up as its the only thing that I could find that was wrong looking.

Started car and all sorted! Lag reduced by half turbo sucky whistle almost completely gone, earlier smoother power and quieter car. INSANE!!!!

LOVE THIS CAR :) Hope it helps in future!
 
CrispyEdd said:
She's been a bit laggy and turbo coming in heavy and ferocious, so suspected sticky VNT or shot turbo.
First run on motorway and she's flying, too good it turned out! Up a hill at 70MPH behind aa= Porsche Boxster 718, I put my foot down shot past and then all turbo power lost - into limp mode?!. GUTTED, a new car - turbo issues - classic rookie purchase I thought, as I let the Porche 718 back past pretending to fiddle with stereo!

Restarting engine gave turbo back again. Quick check on forum....

Checked and traced all the little pipes off the N75 vacuum manifold on offside inner wing (black plastic box with 6 pipes), unclipped the manifold refitted it. All looked good so had that feeling of turbo doom.

Then I found the vacuum pipe from the air intake to the N75 manifold, which is just below and infront (toward front of car) the airflow sensor on the big intake pipe from the air filter, it was about 2mm from being fitted flush, so wiggled it gently back up tight.
To me it looked okay anyway but thought I'd better push it all the way up as its the only thing that I could find that was wrong looking.

Started car and all sorted! Lag reduced by half turbo sucky whistle almost completely gone, earlier smoother power and quieter car. INSANE!!!!

LOVE THIS CAR :) Hope it helps in future!
Click to expand...
Always nice to hear about a problem sorted with a simple and free fix, very pleased for you and the car.
 
Ahh so it's back, I thinknits classic sticking variable turbo. Will try strong turbo cleaner, forte. And report back.
 
My ATL does this 2 or 3 times a year. If I'm due a run up north it sortes itself out if not it's my cue for a tub of cataclean? (Other brands available)! I put it down to pootling to work and back and the fact there's no motorway in Cornwall and I don't even touch the a30(duel carriage way).
Worked for the last 5years of being down here. Can tell it's about to happen as it's sluggish above 2k rpm a week before
 
Running through a tank of fuel at moment with two bottle of forte turbo cleaner in. So far only 50 miles in limp mode occurring about 78‐82mph under load or not. Get a lot of turbo warbling noise I noticed, not whistling. Ut seems to go okay. If it wasn't so damn hot I'd be out more but air con broke ??
 
So ! I'm three quarters through a tank of double strength forte turbo cleaner. The car is running smoother the turbo lag is reduced and smoother, power coming in lower revs than before. The limp mode has changed though, there is only one situation now that causes it. ? once I hit 84mph its limps with eml. I can floor it in every gear up hils etc and it's pulling well its purely 84mph flat or uphill when it kills the turbo boost.

So - any ideas? Air flow, fuel flow? I don't have a code reader for a while so working on feel!!

I've changed the oil oil filter see pic!! And air filter plus timing chain and sorted oil leaks.
IMG-20210725-WA0000.jpeg


Thanks for any help as always.
 
Without a scan no relevant information.

Not reaching 88 may be the flux capacitor shutting down the turbo - No just joking. Perhaps the vanes in the turbo are still sticking tripping the EML, more use may help the vanes unless damaged. Have you tried the same rev range in 4th gear to pin it more to RPM rather than road speed?
Have a good look at the turbo air outlet pipe and make sure all connections are good and air tight. One in particular to check is the lowest one where the bracket secures the air pipe to the sump. If the bracket is missing or broken that area can leak and also put extra strain on the bottom fitting on the intercooler. This in my opinion causes the lower end cap of the intercooler to be flexed and crack blowing out the seal.

I certainly do not recommend doing this at speed but does cycling the ignition clear limp and EML light? Could even be ASV issue.



Still want to know what make you think this is an overboost issue without any errors?
 
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Great info, lots to digest there, given age I'm sure the pipes somewhere won't be 100%. Yes ignition off and it resets again.
There is a clip lower bottom left of engine just before intercooler I packed it with blue roll to firm it up a bit.
I've checked rpm in all gears and loads it's bit odd. I'll get some codes and change little vac pipes see where it takes me, 1888 maybe
 
audifan said:
Without a scan no relevant information.

Not reaching 88 may be the flux capacitor shutting down the turbo - No just joking. Perhaps the vanes in the turbo are still sticking tripping the EML, more use may help the vanes unless damaged. Have you tried the same rev range in 4th gear to pin it more to RPM rather than road speed?
Have a good look at the turbo air outlet pipe and make sure all connections are good and air tight. One in particular to check is the lowest one where the bracket secures the air pipe to the sump. If the bracket is missing or broken that area can leak and also put extra strain on the bottom fitting on the intercooler. This in my opinion causes the lower end cap of the intercooler to be flexed and crack blowing out the seal.

I certainly do not recommend doing this at speed but does cycling the ignition clear limp and EML light? Could even be ASV issue.



Still want to know what make you think this is an overboost issue without any errors?
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Taken overboost off description, just felt like it with lag it had then the surge followed by limp. Now it's settled out.
 
Never discount the fuel filter with these issues - also an easy/cheap replacement that is often forgotten at service time.
 
Thnaks Andy, I checked the history and its 30K since last changed, not sure what a good interval for fuel filter is but I have parts now to change it all over properly using the guide on here. Will do that next adn have ordered 5M of 4mm silicone hose to rpleace as many vacuum pipes as I can get my hand to. Will report back.
 
CrispyEdd said:
Thnaks Andy, I checked the history and its 30K since last changed, not sure what a good interval for fuel filter is but I have parts now to change it all over properly using the guide on here. Will do that next adn have ordered 5M of 4mm silicone hose to rpleace as many vacuum pipes as I can get my hand to. Will report back.
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Is the tubing thick wall ? If not the vacuum can collapse it !
 
Not sure they are samco turbo vacuum boost hoses so hopefully man enough. Will see when the arrive what happens. Do you have a link to what you would recommend at all? Just in case.
 
I would suggest fuel filter change at 30k is likely prudent but wont be causing the issue. Mine had never been changed in 120k and was causing fuel starvation not long after I bought it back in 2017.
 
cheechy said:
I would suggest fuel filter change at 30k is likely prudent but wont be causing the issue. Mine had never been changed in 120k and was causing fuel starvation not long after I bought it back in 2017.
Click to expand...

Broadly in agreement with 30K, mine started causing problems around 75K, but it will depend greatly upon the quality of the fuel and more importantly how much mositure is in it. The mositure can accumulate as a black slimey goop in the filter and definitely affects flow.
 
CrispyEdd said:
Not sure they are samco turbo vacuum boost hoses so hopefully man enough. Will see when the arrive what happens. Do you have a link to what you would recommend at all? Just in case.
Click to expand...
If it’s Samco vacuum tubing it will be fine ?
I just bought 5m from TPS
 
Still haven't fitted vacuum pipes yet. Changed fuel filter today. Have now run a double shot of forte turbo cleaner, one tank of injector cleaner, and now just starting a tank of single strength (correct) forte turbo cleaner. After that I may try a diesel purge clean as alerted to by @depronman . I can report the car is now much much much better and responsive but did still limp at 3800 rpm in third up a hill yesterday. Turbo also warbling a little less (sounds like wind blowing hard through a small window gap) but whistles a bit. Likely needs new innards. Fuel filter below full of tesco finest. I only use premium diesel. Average 59.6mpg still on computer.
 

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Side issue: when I took my ‘54 plate ATL to WOM last year, Rob strongly recommended a turbo rebuild. Not cheap, but recommended after their experience fixing @Skipton01 ’s similar car following turbo failure

Andrew
 
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