The 1.6 Zetec in my Focus really doesn't like to start up. When I turn the key it takes between 5 and 10 seconds of cranking before it will fire up. The battery is fine and a mechanic friend of mine tested the starter motor with a multimeter and said it was OK. Very rarely it will will fire instantly.
It has a bit of a flat spot just above tickover and when in neutral is impossible to hold a constant amount of revs between 2,000 and 3,000. If you try and hold it in that range the revs will just drop away. You have to really put your foot down to even reach 3,000 but when it does the engine goes mad and the revs fly up near the redline because the throttle is pressed so much. When in gear it has no problem holding revs at any level although the flat spot is evident when moving off the line.
It also run very rich, when you start it up there is a very strong smell of petrol at the back of the car and this smell remains even after a good run.
The car has a full Ford service history and in the four years that I have owned it I have replaced the ignition coil, spark plugs, ignition leads, lambda sensors myself. I've tried Magnecor ignition leads too (this went horribly and the engine wouldn't even run and gave off some awful smells). I've even taken all the ignition parts from a friends 1.6 Focus that runs perfectly but it makes no difference to my engine. The bits from my car run perfectly on his car.
I've run all kinds of fuel treatments through it, tried K&N panel filter and a K&N cone filter and none of this has made a difference.
My local Ford dealer has no idea what it might be and I've hooked it up to an OBDII cable and a diagnostics program on my laptop but it shows no faults and all the sensors seem to be working.
I thought I would try asking the people here as you all seem to have a great deal of knowledge about engines