2001 Ford Focus 1.4 starting/idling issues

My parents have a 2001 Ford Focus with a 1.4 petrol zetec-se engine. As a mechanic i am very familiar with the Zetec-se engine as my Ford Fiesta has the very same.

The trouble with the Ford Focus is this; when you go to start the engine (obviously after allowing the pump to prime) the engine takes a few revolutions to start, and usually starts within 3-4 seconds. It also smells extremely bad of petrol once started. When idling, it idles very lumpy however it drives absolutely fine nice and smooth, but does have a blowing exhaust kind of sound.

I have done the following to diagnose the problem;
Tried to pull the code from the engine light, and my scanner says “N/A”
Tried a known working set of HT leads and Coilpack
Tried a known working set of spark plugs
Tried a known working Idle Air Control Valve
Tried a known working Throttle Position sensor
Removed intake manifold and replaced gaskets, same with the throttle body
Cleaned out throttle body
Cleaned Manifold absolute pressure
Tried a brand new battery
Replaced all vacuum lines around the engnie

This vehicle has had a brand new mid and rear section of exhaust fitted less then 2 days before i bought it… incase this may have any impact on the poor idle.

I suspect it to be one or more leaking fuel injectors, as this is all i can think of what would cause a poor idle, poor starting, and smell of fuel. I believe one or more of them to be leaking into the cylinder(s) while the engine is off, thus the smell.

Another point i should maybe make, is after a short 60 mile round journey i rechecked the plugs and 3 out of the four were very black and sooty which tells me its running rich. Also, another tick on the faulty injector list.

Would anyone else be able to advise me here? As i would rather not be thowing money around, that and the fact this has me really puzzled!