Hi guys, I bought a focus estate 1.6t 150bhp last October which has been a constant source of problems. I never wanted it but had to buy in rush. So it has what feels like an intermittent misfire or hesitation when accelerating. There's no pattern and only happens under medium to hard acceleration but it does seem to be getting more frequent now. When it happens it feels like two or three misses per second and continues until you lift off and doesn't usually happen again in the next gear but can sometimes. The car had one previous owner from new with a very full service history (not that it makes much difference I know). Any help or previous experience would be much appreciated. Cheers.

Spark plug, coil, or lead problem? Try the simplest one first - are all the plug caps on tight? Not sure how much of a DIY-er you are, especially with modern cars, but your local garage should be able to fix it I would think. I wouldn't recommend the old test - touching each plug lead in turn while the engine is running to see which one flings your arm up - voltages might be a tad higher these days!

Yes, check the obvious first

Plug condition, they don't change them until about 60,000

Leads and coil pack or coil on plug connections

This engine does suffer with head gaskets though, so compression check next

fuel filter??? Under light acceleration enough fuel can get through, but not under med/hard acceleration. 

A quick glance at the service history should show whether the plugs, fuel filter, and other components were replaced when required. What year and mileage is the car? Reason I ask is that my MX% has a 60k/4 year spark plug change interval, when the car was 4 years old it had only done 25k (12k for its 1st 3 years and 12k in my one year!) and I had to insist that the garage (main dealer) fit new plugs - they intially wouldn't 'cos of the car's mileage, I insisted 'cos of the car's age! Maybe your service history shows similar anomalies. Including the air filter parhaps?