HI.
Just to throw another ball in the pitch....
Noting that its a 94 wrx and assuming that perhaps with age.... the vehicle may have some perished rubber hosing, mainly that, to and from, ure intercooler. It would be advisable to inspect the condition of these as any signs of decay will cause problems under hard acceleration/driving and may not be apparent under more sedate acceleration.
Check any other such hoses that are subject to varying air pressures also.
This could be the easiest thing to check before buying and or swoping parts that may not be required.
Recently had experience along these lines and this proved to be the cause.
