I've just rebuilt my scooby engine ,because the head gasket had gone .
but since putting it back in , its running all lumpie .
the revs go up and down

 

Model year ?

 

its an M reg wrx.

 

check inlet manifold gaskets

 

cheers , but it was replaced , when the engine was rebuilt , only done about 200 miles since

 

knackered MAF?

 

unlikely ... air leak ?

 

I would buy a can of brake cleaner and start the car.
Sounds like an airleak and if you spray at the intake manifold and wiring it should react if it has a split hose or leak somewhere

 

cheers guys , i'll give that ago

 

is the oem fuelpressure regulator stil connected with the inlet manifold btw?
That also give's a very lumpy idle

 

Explain that brake cleaner thing again?

 

in english please

 

He's refering to the vacum line from the manifold to the fuel pressure regulator. Locate the FPR and then check the vacum line is on.

It does sound like some sort of vacum leak (which is why I suggested the inlet manifold gaskets) it may be worth (while you're looking) getting a piece of hose up to your ear and while the car is running use it to search round the inlet manifold to see if you can hear any noticeable air sucking noises. Check round all inlet ancilleries and the bottom of each side of the inlet manifold (where it bolts down to the heads)