Brake Servo/Vacuum problem

[cris_b]

It's been a while and rather than coming back on here to show you photos of shiny bling wheels, it's to say that all is not well with the S3.

Four new tyres (Eagle F1s) after the front Pirellis wore out on the outside edge (down to the carcass (turned out that the tracking was out by 16.5 degrees!) and then a few weeks later a blow out on the rear offside meant the rears needed replacing too

So sorted all that out and now there are engine problems. Car is fine under normal driving until you floor it or even accelerate moderately fast. The symptoms are that the acceleration is hesitant with loss of power and then it comes back on tap in stops and starts.

At first I assumed it was a fuel starvation issue, but running injector cleaner through the system and several full tanks of Optimax have not cleared it. Then I suspected a turbo/airflow related issue and a vacuum leak.

Replaced the main hose and the two intercooler pipes with Samco jobs and put in a Forge DV. This seemed to make it better, but the fault was still there. Not long after one of the speed sensors went on the front nearside front wheel so it went into the dealer to get that fixed (ABS and ESP warning lights had come on).

Dealer spend two hours looking into engine problem. They cannot see anything obvious. Diagnostics check reveals it is pulling more air in than normal so they suspect that it is a vacuum related problem. Turbo is fine, no other errors came up on the VAGCom or what ever else it is they use to check such things.

The head technician *thinks* that it could be a brake servo vacuum leak. He said this is a common fault in S3s but I had not heard of this before? Anyone else had this issue?

His only other hint to this is that the brake perdal feels 'spongier' than it should. I'm not sure why/how the brake system works off the same vacuum system as the engine, but that is what they're implying.

Proposed solution is that the car goes back into the dealer for further tests at the diagnostic labour rate £85 per hour. They will need to get the car up on the ramp drop the engine out and test it fully. if the brake servo is the suspected fault replacement is £300 for the part and the associated labour. Probably looking at £1000 all in.

Any comments suggestions welcomed...

[DuncS3]

What about MAF - thats a common culprit and a relatively cheap part to replace - also you can test anyhow by unplugging it and see if the stop start hesitation goes...

Not heard of the brake servo problem ever before in 3+ years of forums - not to say its not that but...

Dunc

[sitas3]

I think you need to go to another dealer - the only way I'm paying for my engine to come out is when the car needs a new one! there should be no need to remove it. How do they propose to test it?

likely suspects which they must check before even considering unbolting engine mounting bolts are:

MAF (easy to swap to test)
N75 control valve (this controls the turbo actuator)
Turbo actuator itself including vacuum pipe
spark plugs/coil packs (try a new one on each cylinder in turn)
N249 valve and all vacuum pipes between this and the N75 valve (these also have a relation to brake vacuum)
both EGT sensors
Fuel system (injectors, regulator/pump/returns)
Electronic throttle control valve/unit

Some of the electronic control valves can be tested via Vag-com or the dealer's computer.

Let us know how you get on.

[bakerdcb]

I had similar symptoms on my S3 and the first thing we tried was the MAF (diagnosed by Dialynx) Keith swapped it in minutes and everything was fine again. This IS a common fault on many Audis, including S3's- not aware of the problem which has been suggested to you though. New one on me.

[cris_b]

Thanks for the comments, I was I think understandably hesitant to commit to their proposal so it is reassuring that you guys were thinking along the same lines.

Actually having a list of thinks for them to try first is a big help - I will keep you posted on how I get on once the car goes in again next month...

[Scotty]

Sounds like the leak I had on my TT. See HERE

p.s. Sorry there's no pics. It's the W shaped hose at the front left top of the block.

[moose]

there was a recall concerning the servo vacuum pipes spiltting and the one way valve malfunctioning, get these checked, but as everyone above has said - unplug the airmass meter and drive the car - this is one of the most common faults,after that the temp sender, in rare cases the fuel pressure regulator can get dirt in it and give to high a pressure.if these dont show the fault then there are several other areas to look

[cris_b]

Update:

Well for one reason or another I still haven't had this sorted. Largely it's because I've been too busy and most of my driving has been motorway based and this hasn't been an apparent issue. There have been a few A-road sorties that have reminded me that this niggly problemn is still there.

In the end I picked up a brand new MAF Sensor off eBay for £40 and I have fitted this. It has made absolutely no difference so I am now going to start working through the other suggestions.

[AndyS3]

Hi cris

If u have a boost leak due to the brake servo there is a good chance its this hose, its common for this hose to split in the U bend. I have replaced mine with a samco 135 degree silicon elbow. I cant remember wether its 11mm or 13mm, u need to remove the orignal one to check it properly so measure it then.

http://www.demon-tweeks.co.uk/products/ ... AME135-6.5

[cris_b]

Hi Andy

Thanks for the tip. I had Paul at the Car Care Centre in Padfield nr Glossop take a look at it when it was in for it's MOT. Paul's shop is a great Independent firm I used before when I had my Pugs. He had it hooked up to a diagnositics computer that read the ECU memory and this identified a misfire as being logged.

Audi were out of coilpacks, so he put in a new set of plugs and it completely transformed the engine. Closer inspection reveals that the plugs have probably not be changed from new. That's 65K on a set and they were looking very worn. I've taken some photos and will post them up here soon.

Really miffed about:

a) Audi claiming to have run a diagnositics test and having missed this simple thing.
b) The car having done 65K and never having had the plugs changed (from what I've read this should have been done at 20K and 40K, but probably wasn't because they're difficult to get at).
c) The fact that the service also revealed that the rear disc pads were changed, but the discs weren't - but needed to be - when it was last done. That'd explain the shoddy braking as they are very 'lipped' on the inside surface.

Anyway car drives like a dream once again now and I'm thinking about an AP Racing brake upgrade and track days

[cris_b]

Spark plugs picture:

[DuncS3]

I believe plugs are meant to be changed at 40k, not 20k, but I had mine changed first at 23k because I was getting a misfire and have just done them again at 42k as I dont think you should run plugs for 40k miles on a 'performance' car

Glad its sorted

Dunc