Problem with cylinders mis-firing? anyone help?

Hi

I recently (abt 1 month ago) bought an 02 reg ford focus 1.6 zetec with 90k on the clock. It has been serviced regularly (every 12K), and has all the stamps and reciepts to prove it. Last week (Mon) i was driving along when i lost all power and the gar began to judder. I towed it to my local garage who replaced the Coil pack and everyting seemed to be fine, however three days later i began experiencing a lack of power through all the gears in low revs (below 3000), but not a total loss as on the monday. I called the AA out who plugged their machine into the car a said that the cylinders were mis-firing, so i took it to my garage again who replaced both the Ignition Leads and the Spark Plugs, however to no avail.

I then took it to a different garage with a diagnostics machine and explained what parts had already been changed. After the diagnostics they have said its a problem with the ECU and that i'd have to contact a different company for a test and possible replacement of the ECU. To date i have spent £30 on a new coil pack, £25 on new leads, £10 on new plugs, £60 on diagnostics and now i'll have to pay £30 for the ECU test and a possible £200 for its repair or a new one.

Before i do this i wanted some advice on whether it may be a problem elsewhere, i have read that the MAF can cause a similar mis-fire however i cannot find it in my engine, also ive heard it may be an electical connection fault somewhere.

Finally if i do have to remove the ECU to take for a test can anyone explain to me where it is located and how i can find it??

Thanks in advance!