I have an 04 plate freelander with the 1.8 petrol engine, It is starting ok, but revs are jumping up and down as soon as I touch the gas. It stalls a couple of times shortly after start when the revs jump down too far

I recently had the upgraded HG and cam belt fitted, (before it failed) including filters, oil and fluids and it was running fine until then. When I got it back this happened. It seems to be much better when it's warmed up. I have changed the Idle control valve and Manifold pressure switch, (only the manifold pressure switch lit up as a fault when scanned)which has improved the issue slightly.

Any idea?

Totally not a mechanic at all but would like some ideas to run past the mechanic.

Cheers!