Hi All,
First post, please be gentle! 
Picked up a 1.8 Focus 2003 5dr on Tuesday and noticed a problem on my way home, whilst I was there test driving it it was fine - no knocks, bangs, rattles or power issues. It had an EML that was said to be for an o2 sensor replaced.
I noticed when I put my foot down to join the motorway the car started misfiring, when I got back I hooked up OBD2 and saw:
Misfire on 3 (P0303?)
Front Impact Sensor
Pre-tensioner fired
(I'm guessing this was previously in an accident...)
My first thoughts were MAF, so I hooked my OBD2 an watched the MAF reading, seems stable and consistent to my other 1.8 focus (2000). Intake air temp was fluctuating wildly between -18 and +15 now and again - but not at the time of the misfire - This seems to have settled down since? Indicator that the sensor is failing?
I took it out for a drive today from cold, been absolutely fine until the engine had warmed up, power down and it's misfiring again - OBD2 program ForScan on Android is flagging misfires everytime I put some foot down. I can slowly build up revs and it's usually fine, the odd jerk.
Idling is fine, doesnt miss if it's idle, even idle revs, just when in-gear and whilst under engine load.
My experience tells me to check the Coil pack, Sparks & Leads, but was wondering if anybody else had these issues or experience? Just before I head out and go buy unnecessary parts :P
Thanks in advance for any replies.
Chris