I have a 914/4 2.0 as well and have been through the entire DJET system, and what ails you can be found but it will take learning the system, reading and doing basically. I am a novice and could do it, so well my car goes on 1200 mile road trips and perfect idle , acceleration ect. ect. But when I first got the car it was freaking stalling almost then it would go .. then again.. Loose battery cable, another time it was the MPS, then timing, then sticking decel valve kept the idle high. So being it could be anything or a combination of things. I would read these links below and check your system through out. Make sure the wiring harness are secured connected ect.. It seems difficult but it is not and once you learn the djet you can repair and analyze issues quickly even on the side of the freeway in the middle of the night.
I would start with checking all your connections because you say it is not all the time..... something came loose..... or could be wearing or failing. And take notice exactly when it seems like stalling is it cold, warmed up ect. Is it at constant speeds or when your taking off from a stop, does it go away when you push the pedal further ect. It is getting worse or just came on all of a sudden.
Report back.. Good luck..
http://members.rennlist.com/pbanders/http://rennlist.com/techarticles/djetronicfuel.htmhttp://members.rennlist.com/pbanders/DJetParts.htmhttp://www.pelicanparts.com/914/technical_...4_20FI_diag.htmhttp://members.rennlist.com/pbanders/Djetfund.htm