1000-2000 RPM flatspot

[mr_grumble]

Hi guys, my names Steve, I know this isn't strictly 'yaris' related but I'll ask the question all the same

I recently traded my 97 Starlet in on a 02 Echo and while I am happy with the purchase I have a small problem I am trying to nut out.

I have a deadspot in acceleration from 1000-2000 rpm. I mainly notice it coming out of 1st and into 2nd, kind of falls right into the deadzone. Coming up to 2000rpm, it's quite a define step back to full acceleration.
Happens both when cold and hot, occasionally for what ever reason it will go away for a gearchange but 95% of the time theres a deadspot.

I initially thought plugs, so I went out and changed them without success. I then went out and changed air filters, still no change.

The vehicle has 75,000 km (45,000 M) and is manual transmission.

Can anyone suggest what the problem may be. I am reasonably familiar with late model vehicles, just don't want to dive in and start replacing bits that dont' need to be replaced, would be nice to be able to have an educated guess.

Cheers,

Steve