Running very rough - is a sensor the culprit?

It's not mine on this occasion.

It's a S Reg 1998 model in question.

OK so a g13b

Have you tried cam sensor? Is it a hard top? Try the orange screw in filter thing on the fuel rail. Clean it out with some brake cleaner this has worked before. I have a full manifold complete if you need sensors.

At that age you cannot read live data without the Rhinopower interface, or the official suzuki one.

There won't be a crank sensor, just a cam one, this will not throw up a fault if it fails, but the rev counter will jump around when missfiring.

Could be a sticking egr valve, but I'd have thought that it would put the management light on.
The PCV valve in the rubber hose between the rocker cover and inlet manifold has been known to cause idle problems, but shouldn't stop it going at speed.

Thanks guys.

More things to try. Will see how it goes.

Had the same problem solved easily. Carb cleaner spray, do lift the carb up from its mounts ( 4 nuts) and spray it well throughout. use a clean rag and wipe it. If the gasket is torn replace it, very important. 15 mins job.
This is a common minor fault , let me know how you get on.

There's no carb. It's FI.