86 vanagon gl,

What happens is when I start up I have this problem where the engine speed goes up and down until I can get the engine over 2000rpm for a couple of seconds or the engine dies, the problem seems to be getting worse as the weather warms up.  I have just installed new plugs, wires, cap, rotor and oil filter(with oil change) there was no change in the problem after the installment of these parts just a little increase in performance.   I would appreciate any ideas you can suggest thank you!