If it's a regular mechanical throttle linkage, it should be easy to check. However, economy gauge in the red when you floor it is a good sign. I'm thinking it's most likely a fuel issue.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.