2001 s60 2.4T. Squirrel damage to fuel injection wiring repaired recently. Also, some vacuum hose repair. Check Engine light still comes on and Firestone computer indicates that codes read that it might not be firing on all cylinders, but mechanic said that could be a hold over from repair and that it sometimes takes several attempts to clear codes.

So, if my car was running on 4 cylinders, would it be obvious? such as engine running rough? Seems to be OK, except on starting, which is rough for a few seconds.

 

It would be very obvious. I wouldn't have Firestone diagnose it.

 

Try systematically removing a single plug lead, one cylinder at a time,starting at No.1.
You will hear and see when the engines idling changes as you go along which will identify the culprit cylinder if any?