1992 1.5 start/idle problem....

I have a 1992 1.5 manual 4 spd,74k miles. For about the past 3 months everday when I start it for the first time (it never fails to start on the first try) I always let it warm up for at least 2 to 10 mins. Either way it dies when I take off and stop the first few times (hit the clutch). After that it stays started. A related problem is that when it is started it idles at about 1100 rpm untill warm then at 800-900 when idle but when I am coming to a stop after in gear it will go down to about 400-500 then rise back up to 800-900 once I come to a complete stop, furthermore, if I drive it for about 20 minutes, park it without turning the engine off, it will be fine(idle at 900-1100 at all times,stop or go) but if I turn it off even for 1 second it returns to the idle at 500 untill stopped. I recently had the distibutor and computer changed and the timing was adjusted by a proffesional. I changed the plugs and wires after the fact and still no change. Any help will be greatly appreciated.

Also...I installed a tach and spliced into the coil wire going/coming to the distributor, but that was much longer ago than the problems started,could this be a cause?