Only thing I can think of is an air leak somewhere on the inlet side of the engine. Does the idle speed stay steady, or does it go up and down, too? You've had a lot of stuff replaced, so FWIW why not check all hose fittings, clamps etc for snugness and leaks. Tighten any loose-ish hose clamps ... I've noticed on all new cars I've owned that there's always something in the engine bay that's badly routed / loose that slipped thru the PDI.

Good luck

 

Brickboy

All hoses seem well clamped and no leaks are evident. Idling seems normal as well.

Thanks
TONY

 

I have a UK MY2000 Impreza Turbo. From day one the car has had problems with engine surging. This is atrocious when cold (a common problem with Subaru’s I am told), but even when warm it still surges especially when on light throttle (28 in 2nd 38-42 in 3rd) in any gear – especially up to 4th. The car has been in several times for this problem and has been driven by a representative from International Motors called Ken, who has acknowledged the problem. I have had new spark plugs, modified ECU and a new mass air flow meter - all to no avail. The surging is now marginall worse, but the car feels quicker. I need help here, but any cure must not invalidate my warranty.

Help!
TONY BOOTH

 

I think there are multiple fixes for what is effectively a boost control problem. Light throttle between 2.5 & 3k rpm....especially when cold.

On my old my99 I ultimately fixed it by cleaning the dump valve and the boost control solenoid valve and associated hoses. Not sure which was the cause - couldn't be *rsed by this time!

So far, my my00 hasn't done it

Richard

 

I had this, and the thing that fixed it was the Distributor, ie the square thing on top of the engine that all the leads go to.

I did not see how it made it over boost, still don't ,but since changing it the problem has not come back.

 

It does not have a distibutor as the leads are directly connected.