My GTS had a strange phenomena when I bought it. Sometimes, just very briefly, the car startled when running idle. Just as if the ignition was switched off and on again quickly. I looked at the ignition monitoring relay but that was fine ( I would not expect anything there as the problem reset within a few milliseconds) It really behaved like an instantaneous cutout. Not injector alike which is a bit more gradual.
I took off the plugs at the power stage on the front, on top of the bumper. Plugs looked ok, not corroded or anything. I put on some dielectric grease and put them on and off a few times. Also cleaned and re-attached the ground wire there, but I don't think that made a difference. Anyway: problem is gone completely. Seems Ignition got cutouts due to a poor power connection.