Rolling Roads and Sticking throttle

[chewy]

Does anyone know of any Rolling Roads where I could get the GTR tested? I live near Blackpool in the North West so nearer home the better. I would hope the car is putting out about 400BHP. I was happy with the cars performance having had nothing to compare it with but I got a second opinion off a fellow Ultima owner (who was bound to say it wasn't as fast as his) and he didn't think it was revving as freely as it should.
Following a recent trip to the factory for unrelated matters they rang me up to tell me they had changed the throttle linkage and told me that I was only getting half throttle. I was gob smacked and excited. Having now driven it again all I can say is WOW.
However whilst recently trying to scare a young female passenger I scared myself stupid as the throttle stuck on as I approached a T junction ----. On inspection butterfly was stuck open about 1mm but that was enough. I slackened off linkage and all ok but now have lost Full throttle again. I have tried adjusting it but am concerned that it may jam on again if I leave it to tight. Anyone else had similar problems?

[chewy]

I've been having another play with the throttle linkage this weekend and have come to the conclusion that it is the outer cable itself that is stretching when heated. I adjusted the cable a few times whilst cold or at normal running speed but when I started pushing the car harder resulting in Higher Engine Bay temperatures the cable was clearly several mm too short. When cool again the play in the cable had returned. So I've had to find a happy medium which does mean I have a bit of play before throttle comes on, unless anyone knows of any other cable I could use.