Idle problems - try this simple test first
If your engine is having idle problems, before you start worrying about air-flow meters, lambda sensors and constant idle speed actuators (idle control valves) and whacking them with screwdriver handles, try this first... one of the most common reasons for a rough idle is crud building up around the throttle butterfly in the throttle body housing. In both the '94 and '98 onwards 2.0l engines just undo the large jubilee clip holding the large corrugated inlet hose to the throttle body - gently pull the hose away revealing the large throttle butterfly. Get yourself a can of carburettor cleaner (not brake cleaner or WD40) - I use wynn's and spray it all over the throttle butterfly. Use a clean rag and clean all the black crud you can see from the butterfly. Use your left hand and open up the butterfly and spray more cleaner down and around the butterfly - try to get as much of the black crap off as you can. You want to make sure the lower edge where the butterfly closes against the housing is a clean as you can. Don't worry about the cleaner going down into the engine as it'll get burnt off - but don't go crazy with the spraying! Re-fit the large hose to the throttle body and tighen the jubilee clip. Start the engine. Just let it run without revving the engine. Let it idle at 1200rpm then after a couple of minutes it'll drop to around 800rpm. Then you can give it some revvs. If the cleaning has worked the revvs should fall back evenly to around 800rpm all the time and with a smooth idle. My GTV 2.0 1998 kept dropping back to 0 revvs then bounced back to 800rpm - had to heel and toe all the time to keep the revvs up. Cleaning the throttle butterfly solved the problem.
If cleaning the throttle butterfly doesn't work, then it's time to start down the route of air-flow meters, sticking crud-filled/faulty ICVs, lambda sensors - oh, joy of joys!
Just on the point of whacking the constant idle speed actuator with a screwdriver handle, the early 2.0 engines 94-97 had the actuator on top of the throttle body and it's quite obvious, the later engine '98 onwards with the two Bosch connectors on the top of the throttle body, the valve is much harder to get at as it is all part of the MDS. With both versions, try cleaning before whacking - it just might work!