before throwing money at new injectors i would remove the fuel rail with all 4 injectors on it and crank engine over and watch how they give out the fuel,, ie a perfect one should atomise the fuel ie cloud of vapour, so all 4 should look the same, if one dont ie number 2 then you know its that,, but if the car has been driven around for long time chances are might of caused piston ring wash from unburnt fuel in that bore, put id compression are ok then should be ok. those engines have a habit of cracking valves this crack opens up with heat and will cause a misfire to come and go i have seen a lot of them go like this, new engine need not be the answer, ie head off replace the valve and head gasket and head bolts and while in there a new timing chain kit as well as chains need changing around the 60.000 miles mark. also if you were to change engine finding a genuine low mileage engine for that would be a battle and probe over £1500 plus £500- to £1000 to fit it, and that would be on a timing chain already used as such, on those engine because they are expensive to buy is worth the repair then you know you have a good one,