I recently bought a 53 reg VRS with 66K on the clock. When I looked at the car, it threw up

17705/P1297/004759 - Pressure Drop between Turbo and Throttle Valve (check D.V.!)

The dealer has fixed by changing a split hose which I was happy with. The car boost normally at the right time and the power is good.

After getting the car back home, it developed an unsteady idle constantly and threw up

16486/P0102/000258 - Mass Air Flow Sensor (MAF/G70): Signal too Low

This was solved by changing the MAF sensor.

These fixes solved most of my problem but I am now left with a really annoying problem. After I have driven the car really hard and have it stood on idle speed, the unsteady idle comes back and the ASR light comes on and stays on. If I turn the ignition off and turns it back on, the problem goes away. A scan with the code reader threw up both of the codes I had before.

However, if I drive the car normally, the car behaves normally and no code comes up on the reader.

I am not sure what to do next other than checking all the hoses very carefully. I am also reluctant to give the car to a garage as I will be inviting them to thrash my car around and they will probably end up changing parts that don't need replacing.

What do you think I should do next?

The ASR light is often an indication of a MAF fault. I would maybe take it back to the dealer and ask them to check that the MAF they fitted isn't duff

If they didn't fit a genuine VAG MAF that could be the problem. Aftermarket MAF's are notorious for failure even when new.

If the car only throws codes when driven hard I'd say you still have a boost/vaccum leak somewhere. You really need to get VAGCOM/VCDS diagnostic done. 17705 code can be a total nightmare to solve.

Cleaning the throttle body can often cure lumpy idle,& 17705 code.

Replacing the coolant temp sensor if you have the old black type is always worth doing as if it isn't already faulty it will go at some point

The MAF is a genuine one. I might have to take it back to Skoda if the 16486 don't go away. I also looked at the wiring harness and that seem to be fine. Is it true that the sensor takes a while to settle once fitted? If so, how long should it take, it has been fitted for about 2 weeks but I have only just finished a full tank of V-power.

I am wondering what more would I get out of VCDS lite compared to a code reader? I am not prepared to get the full version yet but getting the lite version will mean getting a new laptop as my current one is very old and don't work very well. Is it something that's worth getting?

I think the next thing I will do is to clean the throttle body. Is it essential to replace the gasket between the throttlebody and the intake manifold when I clean it?

MAF should work fine straight out of the box, however it's not unheard of for even a new VAG MAF to be faulty.

Vagcom/VCDS is really useful as it does lots more than read & clear codes. Mine has had paid for its self many times over.

Usually the throttle body gasket comes off in one piece, but it's worth replacing as it's so cheap.

When cleaning the TB it's worth leaving it plugged in with the ignition turned on & the accelerator pushed/wedged down so the butterfly flap is open, makes it much easier to clean properly. When you've cleaned & refitted the TB cycle the ignition, & listen for the whistle from the TB to stop before starting the engine, this speeds up the ECU adaptation process which will be complete after a few driving cycles.

Just cleaned the throttle body but haven't driven it yet. Hopefully it will be better but the throttle body was quite clean to start off with. I am having doubts if it's going to make any difference.

I also went to the dealer today to talk about the MAF sensor that I bought from them. They said I will need to book my car in for a diagnostic under parts warranty. Worryingly, they said that the ASR light has nothing to do with the MAF sensor and that the boost leak has everything to do with the MAF sensor fault code and the rough idle.

I have booked it in anyway but I am worried that they will blame everything on the boost leak and start charging me for randomly replacing hoses in the engine bay. Not sure if I should cancel the diagnostic or not. Let's just hope the throttle body clean has solved everything.

Worryingly, they said that the ASR light has nothing to do with the MAF sensor

Sounds like you need to find a new dealer! There are dozens of threads on here about MAF trouble and most of them mention the ASR light coming on - here's just one I found with a search:

http://briskoda.net/forums/topic/156238-maf-or-not/page__fromsearch__1

I would just pay them for the diagnostic and if it is indeed the MAF then they should change it under warranty - if it has a boost related fault code instead then just pay them for the diagnostic and get the car back as it'll be cheaper to buy hoses and change them yourself.

Btw how do I monitor the boost pressure with vcds lite? I tried this morning on engine and group 11 but it's showing coolant temp.

I've driven it quite hard to work this morning but it didn't show any codes. Maybe the throttle body clean has fixed it afterall.

Group 115 should give you actual and requested boost in mBars:

http://www.ross-tech.com/vag-com/m_blocks/

Seems like it might be ok now though?

Seems to be OK for now, but I think I need to drive it a bit more before I make the conclusion. It was difficult to get the fault code to come up initially in the first place.

I assume group 115 needs a registered version then. I think I need to wait a bit before I get the registered version as I just paid for a new laptop.

Thanks for all your help.

No worries Yep I think the freebie version can only measure certain blocks you need the full version to be able to do everything. There might be a local member to you that has it (check the diagnostics section of Briskoda forums), the full version is £260 and I don't think I could justify spending that much!