Intermittent Power

**eddie_fb** · 27-03-2017,01:10 PM

Hi all,

I have an Audi A6 2006 2.0TDI (BRE) with 185,000 miles on it. Over the years everything that wears has been changed when needed, and very little has failed. It is always serviced on time, and generally well-loved mechanically at least.

I drove from St. Austell to Teignmouth and back yesterday, and it was great on the way there, and most of the way back. However, about 30 miles from home it started to act as if the turbo wasn't kicking in. We'd be cruising at 85ish, then I'd notice our speed would start to drop, pushed on the accelerator and nothing. When navigating steep hills, I was down to 15mph in places. However, every now and then, it would clear, and take off like a rocket! (Well, as like a rocket as an old, high mileage Audi can!) This carried on all the way home.

My first impressions would be that it was electrical, in that it felt as it a sensor wasn't allowing the turbo to spin up? No lurches, or coughs which I would think might happen if the problem was fuel or air?

I've ordered a MAF sensor, as that's never been changed in 7 years, but the air filter looks pretty clean.

The turbo was changed about 4 months ago, due to a weird over-boosting fault, and as I say, when it decides to work, it pulls pretty well considering the age of the car in total.

Would a MAF cause a considerable lack of power, or am I better off looking elsewhere?

Cheers for any help you can give,

Ed.

**Rob69** · 27-03-2017,02:49 PM

I think I'd be looking at the recent turbo replacement, MAF failure tends be more gradual, since you've got one on the way you could just suck it and see though.You also need to check all the basics, vacuum hoses to VNT actuator, N75 valve, and scan it for codes and if you can get VCDS run some logs looking at boost requested vs. boost actual, could also check MAF requested vs. MAF actual but the sudden and intermittent nature of the fault and the recent turbo work would point me to the turbo VNT first. What was the weird overboost fault? was that not putting the car into limp mode similar to what you have now?

**eddie_fb** · 27-03-2017,03:04 PM

Turbo was overboosting to well over 35psi, and the intercooler kept popping. The new turbo seems to have fixed this, and has been running as sweet as a nut for months?

What's the N74 valve do, and where does it live?

**Rob69** · 27-03-2017,03:28 PM

N75 soenoid controls vacuum to the turbo VNT actuator and in turn controls boost pressure, I'm not familiar with the A6 but I think it is in a combined valve block, follow the vac line back from the turbo, might be near the air filter box. On my B5 passat the N75 is on the front of the engine next to the spherical vacuum accumulator.

**eddie_fb** · 27-03-2017,03:52 PM

I don't have VCDS, just a generic OBD reader. The wife has gone out to the car whilst I'm at work, and read the following codes;

P0404
P0401 P
P0404 P

The booklet that comes with the OBD reader suggests these have something to do with the EGR valve, but I don't know when these codes were generated? If these popped up 3 months ago or more, then I'm not sure I should worry about them too much. Also, I was under the impression the EGR really only operated whilst at tickover, so probably wouldn't have much to do with loss of power at a variety of revs?

Blummin diseasels.

**Rob69** · 27-03-2017,04:20 PM

those may be old codes and would likely give you the EML (check engine) and a message on the information screen, on the dash?

**eddie_fb** · 27-03-2017,08:45 PM

We have a likely culprit!

Bearing in mind the EGR codes I thought a look at it might be in order. Took me a while to get it off, but didn't look too bad when I did. Pictures follow, but when I checked the internal gearing there was a few missing teeth.

I've removed an idler gear to show you the lower gearing that actuates the EGR valve itself, but as you can see, the last few teeth have stripped. The motor, and idler gear move freely, and if I moved the lower gears a few degrees then the remaining teeth caught, and everything worked as it should. However, not sure a dob of superglue would hold for long!

A replacement from ECP is currently £128, so I shall get one tomorrow. Anyone heard of HAAS EGR valves?

Wish me luck!

Ed.

**Rob69** · 28-03-2017,07:00 AM

That's a step forward then! You'll need to get the EGR 'adapted' to the ECU once fitted, not sure that faulty EGR has given you the low power symptoms you described in the OP.

**eddie_fb** · 28-03-2017,12:16 PM

Hmm, it turns out the ECP can do a VDO Siemans EGR valve for £204 with the current discount code, so am tempted to upgrade to that one. Anybody had any problems with the cheaper HAAS variant?

And the local Audi dealer mechanics seem to think it won't need coding, so that's one less thing to worry about.