PD130 - no boost until 3000+rpm when cold...?

[muddyboots]

Evening

I have a little problemette with my PD130.
It's a 2002/52 plate Passat with the AVF PD130 engine, remapped, on 93k miles.
Essentially the same PD130, ECU etc as in most Ibizas, Leons etc.

I have no boost at all until the engine reaches around 3000rpm, after which it suddenly takes off. Below 3000rpm it's like a slug, it feels like it's in limp mode and takes an embarrassing age to build up any speed away from junctions, traffic lights etc and I've stalled it 2 or 3 times trying to do so.
When the engine is hotter after driving around, it gets a bit better and boost does start to come in earlier again, but not always.

There are no fault codes logged and no warning lights.

I've been off work for the last 3 weeks and not used the car much, just a handful of journeys, mainly short.
Last week I changed the air filter. Whilst doing so, I noticed some of the vacuum lines were badly rubbed and worn through. Convinced this was the cause of the problem, (not enough vac to operate the VNT mech?) I changed all the vac cables this morning, but the problem still remains. Vacuum seems to hold OK; when I pulled one of the hoses off about 5-10 minutes after the engine had stopped there was a noticeable suck of air, and the anti-shudder valve operates correctly on switch-off.
I also plugged the EGR vac line.
For ages now the engine has been reporting a faulty coolant temp sender, I changed that today and it made no difference.
I also changed the fuel filter today (genuine VW).
One other observation, the EGR valve has been blowing quite a lot of oil out of the little vent hole for some time.

Any suggestions ?
Anyone had the same symptoms ?

 

[T. Spark]

I had a similar problem muddy a few years ago, if I kept it above 3,000rpm it didnt drop it "limp mode" however cruising (or driving normally as most would say!) it would fall into limp mode and have to have a turn off and on again and then dropped down a gear (to get above 3k) to get moving again, not exactly your problem id say but very similar. As it was under warrenty I just got them to exchange the turbo and MAF sensor which seemed to cure the problem, have you ran logs to see air flow? boost request and actual on vag com? see if its actually request boost lower down the rev range maybe and go from there?

 

[muddyboots]

For some reason I have a gut feeling that the last thing I did before I had problems was block my EGR vac pipe. Now that shouldn't cause any problems, but.... Anyway, I unblocked it last night and will see if it's made any difference in 10 mins or so.
Will take the laptop and do some logging

 

[T. Spark]

I blocked the EGR vac pipe some time again and didnt even get a warning light of the engine, nevermind limp mode! Maybe its the pleasure pain theory? Sorry muddy

 

[glynnd]

Defective or part blocked n75 valve, due to drawing in dust etc through the holes in the vac lines
Its located ojn the front of the engine near the timing belt cover
Glynn

 

[muddyboots]

Well...I unblocked the vac pipe to the EGR and all is fine again.



Explain that one !!

Only explanation I can think of is that the EGR is either pretty knackered or clogged, and relies on regular opening/closing to seal properly. It must have been leaking boost
Strange how no faults logged though. Would have expected a charge pressure deviation.

 

[cheshire cat]

Well...I unblocked the vac pipe to the EGR and all is fine again.



Explain that one !!

Only explanation I can think of is that the EGR is either pretty knackered or clogged, and relies on regular opening/closing to seal properly. It must have been leaking boost
Strange how no faults logged though. Would have expected a charge pressure deviation.

coincidence? even with the vanes stuck you would get boost by 2500-3K the egr has a fair strong spring if its leaking oil who knows what the rest is like

 

[glynnd]

Does not matter where you disconnected the pipe, you broke the vac seal in the system.It could still be a faulty n75 albeit intermittent.
Glynn

 

[muddyboots]

I'm certain it's not a coincidence.

I drove several times on different days before unblocking the EGR vac pipe, and the lack of boost was consistent on every trip. On the last trip it never boosted at all, even after a 30-odd mile trip.

I unblocked the EGR vac pipe on Monday and from that moment onwards it has bene fine, done around 220 miles since and it has been 100% OK.

So somehow - disabling the EGR caused the problem. I know that it shouldn't have, but somehow it did.

This reminds me of something I tried on my last Passat.
It always made a hissing sound under acceleration, and - convinced it was a boost leak (it wasn't, seems all Passats do it), I started trying to track down where the hiss was coming from. After no joy anywhere else, I noticed the vent holes on the EGR on that Passat were leaking some oil, so thinking that might be where the noise was coming from, I temporarily blocked up the vent holes, by temporarily stuffing some blutack in them... Went out for a drive - and first bit of acceleration I got limp mode, a CEL, and a charge pressure deviation error. Removed the blutack from the EGR vent holes, all was fine.
I could never explain that one either...

The EGR on this Passat certain spews a lot of oil out of the vent holes, the whole sides and the surrounding pipes etc are covered in it, so something is amiss.

Nic - fancy making me a stealth pipe in return for some beer money ? Would make one myself but just haven't got time...

 

[cheshire cat]

I have a spare 110 egr but don't think it's the same as a Passat one, if we can source a casting/body I guess I could do one, us pensioners are THAT busy!!!

 

[devonutopia]

Sounds like the MAF to me to be honest. Usually they suddenly kick in a lot higher when getting a bit flakey.