4th cylinder works in hectic way
 

Hi,
I have a Honda FRV 2.2 ctdi, 2005 dec. Mileage is 45000km. (FRV has the same engine as Accord has. as far as I know).
I had no problem until now.
I got an immobilizer (IMMO) built into the car at first days of August which worked perfectly for 3..4 weeks.
Recently I realized that only 3 cylinders are working (vibration, less power etc.) with check engine is on.
Honda garage pointed out that there are "electrical problems" related to 4th cylinder. So I went back to the garage which built the IMMO into the car and they deactivated the system.
Then I went back to the Honda garage.
They removed the battery for 30 minutes and made firmware update then they could clear the error from the system.
This solved the problem only for 2 days, so the phenomenon started again...:confused:
Honda garage claims if the problem persists then the injector or engine control board should be changed (money money money).

I think there are cheaper option to solve this issue but the Honda garage is interested only in changing parts at my account.

Could anybody please advice me how to handle/proceed this issue