Sometimes no boost on a4 b7 1.9tdi

**Mrklynch** · 14-09-2016,11:01 AM

Hi guys.

Recently purchased a 2006 A4 1.9tdi. Car runs and drives fine but on occasion there is a boost issue, Sometimes taking off in 1st gear there isn't any boost and no lights or anything but 2nd and rest of gears boost is back. Sometimes will driving in other gears the boost isn't there either but if I do a quick blip of throttle (foot fully off then fully on) it brings boost back.

Plugged in to my own Delphi and it showed up MAF, Cleared fault and was still same, Drove for few days with same boost fault and plugged in again but showing no faults at all so I'm thinking sticking valve or something?

Full black smoke while problem is active when not boosting but again as I blip the throttle the problem goes away and runs as normal.

Any pointers would be greatly appreciated, Thanks.

**JamieG** · 19-10-2016,09:12 PM

HI

You could try disconnecting the MAF, clear the code and drive, see if the same, sounds like what I had on mine at one point, this was the EGR was sticking open, removal and a good clean sorted it, the valve was stuffed with carbon.

**Mrklynch** · 22-10-2016,09:29 PM

Originally Posted by JamieG

HI

You could try disconnecting the MAF, clear the code and drive, see if the same, sounds like what I had on mine at one point, this was the EGR was sticking open, removal and a good clean sorted it, the valve was stuffed with carbon.

Got new MAF today but still same. When I disconnect MAF plug, It makes no difference either. EML comes on after couple hundred miles and shows fault with MAF which is why I've changed it.

Will remove egr Monday evening and go from there. Thanks mate

**Crasher** · 22-10-2016,09:52 PM

So the Air Mas Metre you fitted was a genuine exchange one from TPS or a dealer? It certainly could be a sticking EGR valve with the symptoms you describe, a boost leak would smoke heavily all the time and a failed turbo would leave a fault code. It would be a good idea to check the vacuum system is leak free.

**Mrklynch** · 22-10-2016,10:23 PM

Originally Posted by Crasher

So the Air Mas Metre you fitted was a genuine exchange one from TPS or a dealer? It certainly could be a sticking EGR valve with the symptoms you describe, a boost leak would smoke heavily all the time and a failed turbo would leave a fault code. It would be a good idea to check the vacuum system is leak free.

Was actually a 2nd hand MAF which was only on car for about 6 months, car was driving perfectly and was only being broke because of minor rear end shunt.

Would a boost leak not cause it to be low on power all the time?

A simple way to describe it,, If I'm facing up a long hill, Take off in 1st which would be low on power, 2nd gear low on power with slight shudder but as soon as 2k revs it just
takes off on full power, If I changed into 3rd and revs dropped below 2k then same would happen again and will happen in every gear, But if I blipped throttle while under 2k
then that will also bring back full power.

It does smoke a fair bit when the problem is there.

Also, I just noticed recently if I listen carefully, When I'm sitting idle and give car small rev, I can hear a small are dump as revs settle back down, I don't know if that is normal
but it's very very faint and basically sounds like a toooosh dump valve

**Crasher** · 23-10-2016,05:20 PM

Sorry I didn’t make it clear, I was pondering that a boost leak or a sticky turbo did not match your symptoms. My normal rule is “no codes, no power, new AMM” but unless I know the AMM is brand new and genuine I won’t trust them, even then I have had a number of genuine AMM’s be faulty straight out of the box. What is the VAG part number on the AMM? The EGR valves on the BKE/BRB can get horribly clogged up.

**Mrklynch** · 23-10-2016,06:02 PM

Pretty sure it's a genuine one, I'm out this evening so can't get part #. It was working perfect on friends car so can't see why it wouldn't work ok on mine?.

Yeah read a lot about the egr's on these and I'll be going at it tomorrow evening. I've also read that the egr can throw up EML with code for MAF.

After I installed replacement MAF, I cleared fault and made no difference, I then unplugged MAF and drove for few miles but made no difference worse/better.

Should it have thrown code up straight away when MAF was unplugged? It didn't.