OT: Paging VAGisti

Douglas Payne · 2007-12-08T22:58:36+00:00

Anyone got any experience of bother with the VAG 3cyl 1.4 TDI with ~75bhp?Father has one fitted to his A2. Sometimes under load (going up a big motorway hill for instance), it appears to stop producing boost. It's quite all-or-nothing in the power delivery stakes when its working properly and its a bit worrying to drive when it's unhappy.After stopping and starting the engine it seems to clear and could be fine for the rest of the journey. No pretty lights appear on the dash to warn of anything untoward. It doesn't produce lots of black smoke. I think, but I could be wrong that it sounds a little bit different at idle when it's not running right.Has anyone any suggestions of where to start looking for problems?

Dec 08, 2007 25 Replies

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Chris Bartram 18 years ago

I googled it and hit this:

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Yes, it pretty much confirms turbo/N75/vacuum hose problems.

I'd say do the following:

Check all vacuum hoses, esp. to the turbo VNT actuator from the N75 valve.
Check/replace the N75 valve and wiring. As said above, they are not expensive.
Try manually moving the VNT actuator up and down. On a 1.9, that's best from below with the undertray off. I *think* that if you have VAG-COM handy and do an output test you can drive the N75 (and so the actuator).

Which is pretty much what is said above. All of those are easy DIY things. Dropping & cleaning the turbo a bit harder- and I've never done it so can't comment.

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Chris Bartram 18 years ago

Oh, one more thing:

Have a look at this.

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Douglas Payne 18 years ago

Chris Bartram wrote of how to interpret logged fault codes in your VW Audi Polo A2 1.4 TDI 75BHP.

Splendid.

OK, next question, I am reading about N75 valves now and there seem to be about a million different types and a lot of chaff on forums surrounding what the difference between them is. I also seem to have broken TDIClub.com - it's stopped working at the moment.

The same parts seem to be used across lots of VAG engines, petrol and diesel turbos.

What is the difference between the letters? J and C and H and so on?

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Chris Bartram 18 years ago

Dunno, sorry. ISTR that you can change the N75 with the other control valve for testing, or apply 12v and blow through it. I'd probably just go and get one from the dealer though.

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jackhackettuk 18 years ago

Not in the case of my 90bhp non-PD Mk4 Golf TDI, it wasn't - that was suffering with intermittent power loss like this one appears to be, and this was cured with a new MAF.

It also made it *really* economical. :-D

-- JackH

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jackhackettuk 18 years ago

*cough*

(No, I'm not choking on the fumes)

The very same lump is fitted in our Fabia.

As others have said, quite possibly the N75 - like the MAF, these should perhaps be made a service item, as they do tend to go wrong periodically.

As I've said elsewhere, I had similar problems with my Mk4 Golf TDI estate - not the one I've just got rid of, but the one now owned by Pater.

That turned out to be a faulty MAF in the end.

Once you've sorted this, get him a cheapo tuning box for Xmas (1) - has made the Fabia a lot more grunty, and no running problems so far (2)...

(1) =A315 off eBay (2) It's done about 3.5k now with this in place, and no issues.

-- JackH

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