espace power loss, 1989 2ltr petrol model

[nigelcharge]

after driving about 25 miles i get a power loss, as if the engine is not firing, when i pull over and stop for about 10 mins, it goes, i can then drive for about another 25 miles and the same thing happens. engine is not overheating, i have replaced all leads, dis cap, rotor arm, i have just replaced ignition coil, still same problem( should i replace ignition module as well i wonder) any one any idea whats the cause.
thanks
hope it gets me home