The Natural Philosopher wrote:
snip
You need someone who actually knows how to fault find it.

There are garages that have the test equipment.

Thibgs I have had problems with have been temperature sensors and air
flow meters


What some may find useful is the FAQs at
http://www.megasquirt.info/

While most are probably not up to installing said system, the FAQs on
"how to set it up, and why it works" are excellent.