Thank you all for your help/ideas.
Yes I have used the colortune many years ago and it was quite good but did not replace all spark plug types and in some engines with the plugs down long tunnels, impossible to see!
What I was tring to achieve was a tool to use on any car by putting it up the exhaust pipe.

No, my 1990 740 B200e has no cat or oxygen sensor (less expensive bits to go wrong) + plain old K Jet injection (CIS) as a result it manages 119 bhp from a smaller bore B230 of only 2 litres, not a lot, but just about adequate with a 5 speed manual box and giving just over 30mpg average, with fuel at £0.72/litre it needs too!

Might get a used sensor + boss an weld it into front exhaust when it`s changed.
Autospeed site well worth a look.

Thanks again, Colin.