Very liklely CTS sensor, at back of engine below plenum on near side with a block connector on it.
These are always going and it will most liklely go mega rich when they do mine did, blowing out black soot and fouling plugs misfiring as well kept having to rag nuts off it to clear plugs.
About £10 from MATT LEWIS 01922 692424, top man too.
tabetha