I presume you have checked the throttle position switch? Check the resistance of it (it's located on the engine near the throttle mechanism).
Or you can check it like this (if you have an auto): Drive along with gearbox in '3' position. When off the throttle, and you change the gears down into '2' (don't do at high speed! <30 mph) it will bang into 2nd gear and the revs come up immediately.
When on the throttle (even just a little) and you change down into '2', it will not bang down - you have to increase the revs yourself and then 2nd gear will eventually engage.
If you don't get these 2 very different behaviours, your switch isn't working.
2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black