Classic engine revs fault

Hi, I recently got my 1993 classic LSE back on the road. it ran well for a few journeys but has now the engine has started to cut out at a certain rpm. As I accelerate it will rev up to 1800 rpm but then instantly drops to 1000rpm. it will do this very consistently and makes pulling away quite tricky. if I really plant the throttle, it seems to go straight up to higher revs and then runs fine, so the problem seems to be just at 1800rpm. I don't want to drive it with this fault for fear of damaging the engine. does anyone know what may be causing this fault? (its a 93 hard dash LSE with the 4.2 litre V8)
thanks
Will

Distributer fault? i.e. ignition amp or the advance retard weights or vacuum failing?....reluctor ring gap?

Thanks Saint V8. I'll have a look at the vacuum pipes. I think the amplifier is quite tricky to get at but not too expensive a part to buy. I've previously attempted to remove the distributor but chickened out after I tough I might lose the timing etc.

I would say the dizzy as well.

I had a thread with misfire on the classic tried everything... Saint and I had a discussion and the only thing we could come up with was the dizzy.

Replaced it and bingo !

Thanks Ukadamwest. I'm trying to sell the car so would like to get it fixed so that it's running properly. Hopefully it's an easy fix!

Does it still have air on it ?

Yes, air suspension all working fine. No lpg either, just good old fashioned v8 petrol. I always think that original is best with these beasts!

Fault in the throttle position sensor (potentiometer) due to wear?
Appreciate this is a Disco: http://www.lrfaq.org/Disco/Disco.Throttle.Problem.html

I've now changed the ignition amplifier, stripped and rebuilt the distributor. The weights both work fine and I checked the reluctor gap. It's now running really sweet except for the occasional hesitation. I've got a replacement throttle sensor coming and hopefully that will sort it....so frustrating cost otherwise it's just running so sweet

The replacement tps has done the trick. It's running perfect and (sadly) is now for sale on eBay...

Rodent said:

The replacement tps has done the trick. It's running perfect and (sadly) is now for sale on eBay...

Click to expand...

Put the link up, you may have people interested on here.