VW GOLF MK3 1.4SE (no power)

Hi all, i have a problem with my golf, it seems when I put my foot down on the accelerator its laggin like there is no power, sometimes it runs ok. and sometimes when i put my foot down it lags. also on the motorway. it will just stay at 60mph with my foot down to the floor. and sometimes it will cruise over 100mph no problem. I seem to get this problem when my temperature gauge is at half way. it will drive ****. and when it starts to cool down it will gradually get better. but even when im on the motorway and my engine is cool it will still do it. anyone have any ideas of what it could be? thanks

I think my missus has a similar problem. After changing the spark plugs, leads and ignition coil (situation improved slightly after the coil replacement), the actual distributor is next for renewal. I've been told that the hall sensor could be at fault. Not a user changeable part, so an exchange distributor is required, £60 or so from GSF. Not had time or funds to do this yet.