Lumpy at idle

Been using my Exige for a week now (the MR2 wont crank for some reason and I have to admit defeat )

anyway the Exige stalled in traffic the other morning and since it’s been very lumpy and feels like the motor is going to die at idle (just just like my old elan likes to)

Any ideas? I was going to whip the plugs out/clean and give everything a wipe down???

Plugs, air filter, check sparks on all cylinders, had any fuel from remote garages?

Re Fuel - no only buy Esso unless i’m caught out. I usually use Esso super (or whatever the the dearest one is called) but had to use standard on this tank full? Got it from the same place and have done for about 13 years with no probs b4

Certainly could be the juice

thanks for the info