Erratic idle could be either a too rich or too lean fuel situation, or as others suggest, could be a vacuum leak although a vacuum leak usually produces fast idle which cant be adjusted down to 800 or so RPM. Suggest you go to the internet site for VClassics.com and look at their article on D Jet injection system. Lots of good trouble shooting tips. To test this system, you will need a multimeter, a test lamp and maybe a fuel pressure test gauge.

Without knowing any more than whats in your posting, I would test the manifold pressure sensor, temperature sensor # 2 which is the one in the side of the block for the coolant(they rarely go bad), and look for a vacuum leak. My favorite way to do this is with a piece of 1/2" diameter ttubing about 4 feet long. Start the engine, put one end of the tube in your ear and move the other end all around the manifold gasket, the injector lock rings, hose connections etc. Anywhere where unwanted air can sneak by and get sucked into the engine. If you hear a hissing sound, thats it. Good luck