S8 idling 'lumpy'
 

Hi all, this is a bit of a long shot but thought I would ask.

My first real problem has arisen.

Have now done almost 4k miles in the s8, almost all motorway, lovely and smooth but about 400 miles ago I could feel that it was slightly
'Hunting' when cruising at a steady modest speed of say 60/70.. it was barely noticable though.


This morning as I was 10 mile from the end of my weekly 70 mile commute I heard a sound which could best be described as "ppffst" and it the started running really lumpy.

I managed to make the final 10 miles in stop start traffic and it didn't cut out.

Have gone back to it tonight and it started first time, no worries and revs fine, no funny sounds.

Question is this, as I say I know its a long shot but, what are thoughts on a slow 70 drive to get to the garage as I don't know any where I am presently parked up..

Any advice appreciated.

Hmmm initially I thought crap fuel but then after reading the whole post, with a pffst maybe a vac hose

I am thinking a hose too.

Would be under load at 70, not so much in the crawl.

The air sound you describe would indicate something is not sealed or has a hole somewhere. It doesn't take much, might not be easily visible but a tiny hole will rob you of power.

There's a bung on the front of the inlet manifold just above the flap actuators which blocks off a large vacuum port. That can perish and disintegrate and then allows unmetered air in to the manifold which then makes the engine run very lean.

Maybe pop the covers off and listen for anything hissing?

Do you have the ECU light on per your other thread? Have you scanned it yet?

Thanks All, sounds like it wont harm it to much (other than petrol consumption..!) if I drive back so will take the chance.....

any pictures of said bung? I had a look today but couldn't see it nor anywhere missing one