New to this site, but if buy this car will be here more often so Hi all!

My mate has a fiesta St 04 plate
Tempted to buy the car off hi but it has a running problem where if you stop the car, or even dump the clutch the car will cut out.
It will do it constantly when it is cold b it after driving it about 20/30 miles it wasn't cutting out the revs would just drop really low then go back up to idle.

The car has had quite a lot of engine work, high lift cam, mondeo St inlet manifold ect all done by site tech.

I've brought the car into th garage to take a look at it tonight, I was going to take the idle control valve off and clean it but then after some research realised it doesn't have one.

It doesn't sound like it has an air leak but haven't tried spraying anything around the pipes..

Was wondering if anyone has any good suggestions where to start or if anyone has had this problem before.

Thanks for help in advance