Flat acceleration above 3,000 rpm

[Clarkus]

I have a P. reg 1.9 tdi (red dot) Audi A4 with 187,000 miles on the clock which has always performed really well and reliably. Recently the following symptoms have occurred: There is a lower than usual amount of acceleration up to 3,000 rpm, but it is at least reasonably smooth. As soon as it hits 3,000 rpm it goes totally flat and won't accelerate any more unless the car's going down a hill! Going up hill is a complete nightmare as the engine revs drop away until it drops down to about 40 mph after the appropriate gear changes. Having looked on this forum the consencus of opinion on other postings suggests that the MAF needed changing, so I took it for a fault diagnosis. This showed a fault on the MAF, so I tried disconnecting the old one, but it made no difference. I bought a new MAF and changed it myself, but this made no difference either. I took my A4 back to the garage who did a fault diagnosis and it now showed 'no fault' with the MAF. On the recommendation of a workmate I've disconnected the battery for an hour so it can 're-educate' itself that a new MAF has been fitted to no avail. Any suggestions would be very welcome!

[Pete@ECSTuning]

Do you have any idea if your turbo is boosting the same? Do you have a logging tool or boost gauge?

[fourringsrus]

FUEL FILTER /FUEL LINES
AIR FILTER
Just a thought
Stuart

[Clarkus]

Chris,
Don't know and no to the above I'm afraid, but there is no turbo boost gauge on the dash.

Fourringsrus,
Air filter is fine, but I'll check out the fuel line/filter side of things.

Thanks so far,
Clarkus.

[martinA4passat]

Check the cat is not blocked, that will reduce power etc and get worse the more you put your foot down.

[Pete@ECSTuning]

Well if the 1.8t is at all similar it sounds like you might need a n75 valve. The n75 valve controls your turbo's wastegate actuator and when it fails it typically causes poor boost conditions because it is allowing your wastegate to stay open, effectively rendering your turbo useless...

Currently, we have 30 in stock because they fail that commonly. They are even on sale too:
N75 replacement valves - on sale

[Clarkus]

Martin and Chris,
Thanks for your suggestions.
Martin, your thoughts on the cat are very interesting because about the same time that all the power disappeared a strange rattling noise developed on tick-over from under the car which I couldn't find a cause for but sounded like if anything was coming from the exhaust pipe. Definitely worth looking into.
Regards,
Clarkus.

[chris_r]

I've been suffering with poor acceleration high in the rev range. This might help...

https://www.vwaudiforum.co.uk/forum/s...ad.php?t=85623

[HomerSimpson]

Hi Clarkus,
I think that you can rule out the N75, mine went and the symptoms were that reving over 3000 rpm and under load the engine would go into safe mode. I must admit though that the power was down as well.