testarossa idle surge

86 testarossa, 20,000 miles all stock except air pump removed.
starts fine cold.
idle surges between 500 and 1400 rpm every half second.
moderating the throttle does not have an effect, not a sticking mechanism.
warm running is fine.
hot running idles fast 1400-1500
not running rough

connected two vacuum gauges 1-6 right bank running 3in less than 7-12.
switched gauges to ensure not a gauge difference. same result.
suspected fuel starvation so i replaced fuel filter, same result.

currently testing, cleaning and replacing faulty injectors.
have a cis pressure test kit, will check line and distributor control pressures next.

anyone have any other ideas.