HI PEOPLE IM FROM DUBLIN IN IRELAND AND HAVE A 94 WRX I BLEW THE ENGINE AND GOT A 99 ENGINE PUT IN AND IT SEEMS TO BE SLURGING A LITTLE WHEN I HOLD IT AT 3OOO REVS WHAT COULD IT BE ITS DOING MY HEAD IN I CHANGED PLUGS ,RESET THE ECU AND CLEAND THE SOLINADE BUT STILL THERE ANY HELP WOULD BE GREAT THANKS ..IRISH FAN

 

they all (MY99) seem to surge slightly.
mine goes after it has warmed up.

 

The surging when travelling at around 3000rpm is probably just because it's the point when the turbo boost really gets going. If you're cruising at 75mph (=3000rpm in top gear), then the slightest bit of extra throttle causes the turbo to spool up a bit, which makes more exhaust gas, which causes the turbo to spool up quicker... etc. You get the idea! It can be a bit of a challenge to hold it at that speed.

However, most MY99s do seem to surge a bit between 2500 and 3000rpm on light-medium throttle when cold.

Richard