When I first start up my car the engine is lumpy and the idle irratic. When the car is warmed up it runs fine but I can't figure out why this is happening. I'm worried my engine is going to die. I've just had an oil and filter change but that hasn't improved anything.
Can anyone help?

 

A VTA BOV can cause an erratic idle at startup, however it only lasts a few seconds, how long does your lumpy idle last?

 

If you still have the standard airbox fitted, check the piping connecting the boost solenoid to the resonator box. This is a pipe running from the bottom connection of the solenoid to a small connection just under the piping from the MAF sensor.
Mine had come off and caused exactly the same issues you are having. Also check pipes for splits.

Agree with above too, a VTA BOV does appear to cause the same problems if you have one fitted. Best to swap back to the standard Subaru part.

Hope you get it sorted

 

I'll check the piping but I don't have a VTA bov anymore or a standard airbox. The lumpy idle and revs last for about 10 mins until the engine is warm. I leave the car to warm up during this time until the revs eventually go to normal but if I do drive it before its warmed up it feels as though there's no power and there a delay in accelation response. But when warm the car runs absolutely fine.