Wondering Idle
 

My idle on my 1981 280ZX 2+2 speeds to about 1100 RPM then down to 900 then back to 1100. This up down is cosistant and takes about 10 seconds to make the cycle. I have check all that I can find in the manual, but no luck yet. New plugs, wires, fuel filter, air filter, rotor cap. Cleaned injectors. Adjusted valves and timing. Checked for vacume leaks. I get the same result with air conditioning on or off. Any suggestions??? Thanks Stu