Hi guys, on cue my car has thrown another challenge at me. I enjoy it!

I've had a bit of a low rev boost issue for a few months, maybe over a year, where it stutters. No EML.

Last week the EML did come on, and VCDS points to low EGR flow. I've checked all the hoses from the control valve unit, they all look fine, and I've changed the control unit for a known working one. Before the EML came on, the turbo was more audible, which took a couple of weeks for the EML to show. I haven't cleared the codes since changing the control unit, but as the turbo still whistles more than it used to, I'm 99% sure it isn't cured.

So I'm thinking, rebuild the EGR with new seals, or could it be something else? I have a complete turbo unit I could get refurbed, but the car doesn't seem to have changed how it's boosting. I know it's not perfect, but the thing is old and I'd assume it's likely the VNT that has coked up.

Open to suggestions, if it needs something new I'm happy to pay!

On my old Seat altea 1.9tdi BXE (same engine) there is an egr cooler at the rear of engine. On the cooler there is also a vaccum unit. Its plastic. On mine I kept getting EGR flow errors and limp mode. EGR was working fine. I tracked it down to the plastic vaccum unit. It was sticking and not opening fully. It could also be the egr cooler thats choked. The plastic vaccum unit looks like this

On 17/09/2025 at 09:29, Taz1983 said:

Hi guys, on cue my car has thrown another challenge at me. I enjoy it!

I've had a bit of a low rev boost issue for a few months, maybe over a year, where it stutters. No EML.

Last week the EML did come on, and VCDS points to low EGR flow. I've checked all the hoses from the control valve unit, they all look fine, and I've changed the control unit for a known working one. Before the EML came on, the turbo was more audible, which took a couple of weeks for the EML to show. I haven't cleared the codes since changing the control unit, but as the turbo still whistles more than it used to, I'm 99% sure it isn't cured.

So I'm thinking, rebuild the EGR with new seals, or could it be something else? I have a complete turbo unit I could get refurbed, but the car doesn't seem to have changed how it's boosting. I know it's not perfect, but the thing is old and I'd assume it's likely the VNT that has coked up.

Open to suggestions, if it needs something new I'm happy to pay!

It sounds like the issue on your car is due to low EGR (Exhaust Gas Recirculation) flow.

🔧 Possible causes:

• The EGR valve is clogged with carbon deposits and not opening/closing properly.

• Seals or gaskets are leaking, causing pressure loss.

• The VNT (Variable Nozzle Turbo) may have carbon build-up, making the vanes stick or move slowly.

• Small leaks in the vacuum lines or control valve.

✅ Options:

• First, remove and thoroughly clean or rebuild the EGR valve, and replace seals.

• If there’s no improvement, look at cleaning or refurbishing the VNT/turbo.

• Double-check all vacuum hoses and connections.

Since the fault code clearly points to the EGR, the best first step is an EGR clean/rebuild, which in most cases solves the problem.

12 hours ago, Alasdair1 said:

On my old Seat altea 1.9tdi BXE (same engine) there is an egr cooler at the rear of engine. On the cooler there is also a vaccum unit. Its plastic. On mine I kept getting EGR flow errors and limp mode. EGR was working fine. I tracked it down to the plastic vaccum unit. It was sticking and not opening fully. It could also be the egr cooler thats choked. The plastic vaccum unit looks like this

What you’ve shown in the picture is a vacuum actuator (plastic vacuum unit) that sits on the EGR cooler in your Seat Altea 1.9 TDI BXE engine.

• Its job is to control the EGR cooler bypass flap using vacuum pressure.

• If this actuator sticks or doesn’t move smoothly, it prevents the cooler flap from opening/closing properly.

• When that happens, the ECU detects incorrect gas flow → leading to EGR flow errors and sometimes limp mode.

Likely causes:

1. The vacuum actuator itself (plastic diaphragm or mechanism sticking).

2. The EGR cooler is clogged with soot, making the flap hard to move.

3. A vacuum leak in the line feeding the actuator.

What you can do:

• Check if the actuator arm moves freely by hand (with vacuum applied it should pull fully).

• Apply vacuum with a hand pump → if it doesn’t hold vacuum, the diaphragm is torn → replace actuator.

• If it moves but sticks, the cooler flap is probably clogged → remove cooler and clean/replace.

Many times, just replacing this plastic actuator (or cleaning the cooler flap) clears the EGR flow error without touching the main EGR valve.

Thanks everyone. I changed the EGR, cleaned as much as I could in the manifold, but now the car won't start. It turns over, I tried 3 times. I suspect I've got gunk down below, stopping the car from starting. Hoping I haven't bent a valve, I'll take it all off again tomorrow. I'll probably renew as much as I can while it's all off

Check you replaced all the electrical connectors and vaccums etc and there secure and making contact. Weird it wont start after it being cleaned unless you dropped a lot of gunge into intake. It could also be stuck open but car not noticed as it was completey blocked

Alasdair

I'm almost certain everything is connected, I've had things apart a few times, but I'll check again.

I cleaned as much of the inlet manifold as I could, a lot has surely fallen down. There was I'd say 1cm of buildup on all the surfaces, I did scrape quite a lot inside the manifold, I'm not sure how much would prevent the car from starting.

The EGR is new.

I've ordered a used manifold to clean up before taking mine off so can stick one straight on. Would taking the glow plugs out and turning the car over be wise to do once the clean manifold is on?

Is it worth changing anything else while it's all apart? It's likely the last time this car will see this kind of job

Is there any other way to get fluid out of the engine without removing the glow plugs or injectors? The glow plugs are obviously one I'd much prefer avoiding right now!

If it turns over then any fluid may come out anyway unless its hydraulicking. Wonder if you have blocked the cat with gunge and fluid as there is no dpf as far as I know on the BXE. Removal of glowplugs is better done when engine is hot and also better to put some penetrating oil around glowplugs for a few days beforehand. Check the butterfly is operating in the air intake.

Alasdair

It doesn't turn over, maybe cranks once (I tried it 3 times, so it hasn't turned over much if at all).

I used brake cleaner, I'd have thought it'd evaporate sufficiently.

The air intake being the throttle body? I can check this with VCDS. Would that cause similar symptoms to this? Could the new EGR be the cause of the issue?

I checked the oil, it's dirty (due a change, I do it every 6k), but isn't thin or watery. The level seems normal.

I'm going to clean up a spare intake manifold, refit it all and ensure everything is as clean as I can get it without going in the engine. I'm soaking the glow plugs everyday for a few days. There's a local garage who I might approach to see if they'd remove them for me.

When you say it doesnt turn over but cranks once do you mean that the engine actually turns (pistons are moving) but doesnt start or does it turn and then stop turning at a specific point. I wouldnt use starter until your sure there is nothing gone down air intake that could jam pistons/valves etc. Try and turn engine over by hand and see if there is any resistance at any point. Hope that makes sense.

Engine cranking to me is the same as engine turnover but not the same as starting. Brake cleaner should evaporate quickly so doubt its hydraulicking

Alasdair

It reluctantly tried to start, but it only managed what sounded like 1 rotation (if that), like it can't overcome whatever it's trying to compress. Could the garbon gunk be enough to prevent starting? I believe there might be quite a lot down at the bottom of the inlet manifold.

Once I have all the parts I'll take the inlet off then try rotate the engine by hand

From your description of 'only turning once if that' .something maybe jamming a piston or pistons in one or more cylinders One may be full of liquid/gunk and not reaching full stroke before either hitting something or trying to compress liquid. It may be worth loosening the injectors or glow plugs to cause some decompression and see if any liquid comes out . I would turn over by hand until you check out inlet etc.

Alasdair

Glow plugs I'm afraid to snap them, so it's going to be a few days of plusgas / attempting to turn them. I suspect you're right, brake cleaner hasn't evaporated. I'll update once I've got the glow plugs out / changed the inlet

Thankyou for your help it's much appreciated

Cant think of any other way to decompress engine. Hopefully if its brake cleaner it will eventually evaporate or drain down.

Inlet manifold is now off. Struggled with access to the 6mm bolts but perservered.

I'll attach photos, but the inlet is clearly completely full. It seems to me that there just wasn't enough airflow to even turnover.

Not sure how to approach cleaning the ports. Is it safe for me to scrape them or not? Maybe try burn some of the crap off?

Just now, Taz1983 said:

Inlet manifold is now off. Struggled with access to the 6mm bolts but perservered.

I'll attach photos, but the inlet is clearly completely full. It seems to me that there just wasn't enough airflow to even turnover.

Not sure how to approach cleaning the ports. Is it safe for me to scrape them or not? Maybe try burn some of the crap off?

Lots of scope for cleaning! 😆

Is it safe to clean out the ports on the head?

Scraped out what I felt was loose in the head, engine was a bit reluctant to turn over at first but rotated through all 4 injectors firing so the engine isn't seized in any way. Going to take my time cleaning up all the parts and ordered new bolts and gaskets. Should run well once done!

Thats about as bad as I have seen. The reason why I hate EGR systems. Whover came up with the idea of adding diesel exhaust back into engine I reckon wasn't a mechanic. Had an old toyota diesel the same. I cleaned everything up and then blanked EGR. Older engine so got away without telling ECU. It ran fantasticly after cleaning and still got through emisions at MOT. The gunge that came out on mine was like road tar.

Alasdair

1 hour ago, Alasdair1 said:

Thats about as bad as I have seen. The reason why I hate EGR systems. Whover came up with the idea of adding diesel exhaust back into engine I reckon wasn't a mechanic. Had an old toyota diesel the same. I cleaned everything up and then blanked EGR. Older engine so got away without telling ECU. It ran fantasticly after cleaning and still got through emisions at MOT. The gunge that came out on mine was like road tar.

Alasdair

The concept is sound I think but once something goes wrong or the car isn't driven in perfect driving conditions (I'd say long motorway runs so everything burns off), the system does this. It is an old car mind, I expect it to get dirty again but not to this extent again

Refitted everything before the new gaskets / bolts come. Sounded horrible at first, turned it off, started again and runs fine.

The glowplug harness disintegrated so I've got a new genuine one coming. Does anybody know where it connects? Does the ECU need to come out to wire it in?

Not sure but there may be a timer/sensor unit for the glow plugs that it connects to. Had them on a few old diesel vans.

Think the one on the 1.9tdi looks like this

Its usually in the engine compartment somewhere. I think the MK1 were under dash

Alasdair