This is almost exactly my symptoms as well (Esprit 89 SE). I just had the manifold replaced (engine out) so all cables were disonnected. Now what happens is the the car seems to run ok "MOSTLY" provided I dont thrash it. however after a long run when I come to idle the revs stay at 1800 ish, I can blip the throttle to no avail.... However , If I switch off / on then the idle is instantly correct. Did you get any resolution to this.. I put a new Lamda sensor on last year and it seemed to be cyclng correctly. BUT is not an original, its one specified in lotusworld. However I will re-check the connections to that sensor . Anyone with any ideas I would appreciate some guidance. I broke my ALDL connector (sat on it) so just soldered some new transisitors on it. Will try it out tonight and see what the sensor says..