idle problem :/

[hillary2005]

Just had a lot of work done on my S3 including new piston rings, rebuilt head and new turbo

Got it home yesterday and its idling funny. Best way of describing it is as if its got a set of harsh cams on it!

It won't settle down and idle normally its constantly up and down and it seems to be hunting for air. When driving a long out of boost the boost gauge is saying 20psi of vac however on idle its up and down too around 10 and 0

I know its got a maf sensor fault could this be its problem or should I be looking for split pipes etc?

 

[HTC]

A vacuum leak would cause this. Have a look to see if a pipe is split or not connected properly since the rebuild. Throttle body may also need re-aligning.

 

[Welly]

If it's not a split vac pipe, I will eat my hat.

 

[hillary2005]

Can anyone point me in the right direction of the vac pipe? Bit of a gormo when it comes to all these pipes

 

[Welly]

Ummmm, there isn't really 'a' vac pipe. There are a series of vac pipes.

A vac pipe refers generally to any of the pipes which is connected to the inlet manifold. These are the pipes which have a vacuum feed from the inlet manifold on idle.

You will find 3 pipes under the inlet manifold, 2 small and 1 large. Check these.

Check the pipework around the diverter valve, and N75 valve (these are up the back of the engine).

Being an S3, you should also check the N249 valve pipework on the top of the engine, underneath the black plastic engine cover.