1994 Honda Civic Idle problem and stalling

Engine Mechanical problem
1994 Honda Civic Two Wheel Drive Manual 112000 miles

Hi, I have a 1994 (M reg) Honda Civic Lsi, with a 1493 engine. I am having some considerable problems with the idling on this car, I replaced the idle control valve with a second hand one, and it seemed to rectify the problem for a couple of weeks and now it is even worse! I have to keep the car above 2000 RPM for it to move anywhere without kangaroo hopping or stalling, initially this was just in 1-5th gear but it is now happening in reverse too. The car idles at 1000 RPM when stationary, and doesn't move from there, however when I press the accelerator to put the revs up to 1500 rpm and then let my foot off, when stationary, there is considerable die back and it drops to 0 and the car stalls, sometimes it manages to hang on and get the revs back up, but you can hear it struggling.

The car has recently been in the garage on the diagnostic machine and it is coming up with an idle control valve fault. The blokey there wants to check the wiring from the valve to the ECM, as he thinks this may be the problem, is the wiring likely to cause this problem, or would it be better just to get a new valve and fit it?

Also it was picked up that I need a new Cat converter for the car, again the blokey said this can cause the problems I am experiencing, are they easy to replace for a novice or should I just let the garage do it? And can the cat cause such problems with the idling?