3.0 tdi hunting overrun

[jubbly]

Hi all,

I changed my car back to a 3.0 tdi two weeks ago, it's the 233 engine 171kw, Auto box and quattro 100k miles.

It had quite a few dtc's which have now been sorted, including glow plugs and inlet manifolds low limit.

After I changed the inlet manifolds I was hoping the MPG would improve, i'm barely able to get mid 30's at 70 mph, my earlier 165kw would do 40mpg at the same speed, I though the 171kw was a more economical engine.

I also have an issue with the revs hunting/surging on overrun, if I'm driving at between 25-55 mph and come off the power to come to a junction etc the revs jump up and down around 300 rpm every second and you can feel the car jerking at the same time.

The only fault left on the car is the drivers side enigne mount has a fault I can't clear and the drivers side electric heated mirror showing as open to ground.

Any body any idea's on where to start looking? MAF, throttle body?

I can post the dtc's later.

Other than that I'm happy with the car

Cheers

Paul

[joedredd]

Have a look at this thread;

BMK 3.0 TDi hunting erratic idle revs ( Have I got the most lemon A6!!! )!!!-)

[jubbly]

Thanks, I've already spent quite some time reading the whole thread, mine doesn't hunt at all on tickover, thats rock steady, only on the overun, I haven't had any luck in finding anything other than tickover hunting on the forums.

[TheMatador]

Hi, I've got the same setup. Rarely got more than 33mpg on the motorway. Interestingly I think the mpg got better at about 85mph. The engine seemed to be just getting into its stride.

On the overrun, on mine the revs jump about a bit when I take my foot off the gas around 40mph in 3rd or 4th. I think it's the torque converter getting a bit indecisive. I don't think it's the throttle making it rev, it's like in a manual when you feather the clutch and bring in the engine braking. Is that the same thing you're seeing??

[jubbly]

Hi,
yes that sounds like it's the same thing. Even if i just keep on the throttle a little i get no variation in revs, hopefully it's something i will get used to. It didn't do it on the test drive, typical!

On the mpg side i've turned off my aux heater and mfa shown 39.7 for journey yesterday, it did go upto 43.4 so i'm hoping thats better.

[Cwizard]

Hi, i've got the same thing happening to mine. I thought my gearbox was stuffed up. After taking it to Audi for a service they told me its the pulsation dampener thats causing it. Which would cost around $200 including hands.
I haven't taken it yet. I will when i go in to change the front brake pads. So i don't know if it will cure that rev fluctuation while decelerating... Good luck.

[TheMatador]

Aw crap - not another thing that might be wrong. This is my first auto - only driven manuals until I got this one. Thought it was a bit odd when I first experienced it but thought it was just one of those things with an auto. I've had it 3years now and gearbox is still silky smooth otherwise (other than the occasional lumpy downshift - usually to 2nd when i give it a bit of throttle just as its changing).

So what's a pulsation damper??

[Cwizard]

The person questioned knows nothing more than the person questioning... lol
No idea mate. If i get it fixed eventually ill update this forum with it.

[gupsterg]

So what's a pulsation damper??

Link:- http://en.wikipedia.org/wiki/Harmonic_balancer

[jubbly]

I did read yesterday, but now i can't find the link again, that the pulsation dampener can give upto 10% better mpg, my mfa is not reading near the correct value, as it's based on fuel pressure and the pulsation dampener controls the pressure, i'm thinking it maybe the answer.
I will look on ETKA when i get back from easter and see if I can find it.

I know I can adjust the mfa reading from vag-com but as I've ordered a bluefin also i dont want to start messing until everything is bedded down.


PS Happy Easter all!!