I have a very lumpy engine on my (unmodified) 99 UK Turbo. only occurs around 2,000 - 3,500 rpm and then all is ok when the turbo kicks in....any ideas..???

 

Hmmm, I'll watch this thread with interest. I have an MY99 with full decat and tek2.5 and I find it to be the same. Its a pig when cold off boost but as soon as the turbo gets involved it seems fine

 

Every Impreza I have been in is crap off boost, particularly when cold compared to quality NA engines. Reluctant, slow, painful and not very smooth. Comes with the territory of a compression ratio of 8:1 IMHO. However, if yours has got worse than previously or is worse than other Imprezas then you need diagnostic checks on it with suitable equipment. There are several things that could cause this problem and you are only guessing.

 

Agree with JB, could be a number of things.
Checking the fuel pressure is also worthwhile, I found that an extra 0.2 bar made the engine far more responsive, especially when cold.

Andy

 

Can I put a slightly different "spin" on this.
My car is fine until I reach about 4500 rpm and then it starts to judder/misfire and keeps on being rough to 5000 rpm with very loud misfires. If I back off and then try again it may not happen the second time - but it might. Problem definitely less when going down hill ??
The car is a MY94 WRX with an HKS air filter and Japanese wide exhaust. Recently changed petrol filter and cleaned out the fuel tank and replaced a faulty coil. Boost is normal.
So does anyone have a suggestion ? It slows my overtaking as I'm never sure of a clean response !

 

I think it's just a trait of the Impreza engine like John says. I think it feels worse below 3000 than it actually is though, because of the massive rush when the turbo comes on song. It's like night and day, you get such a shove in the back at around 3k that it just feels crap until then. Does that make sense?