95 throws error code 35

I have a '95 K1500 Z71 350 TBI that will turn the Service Engine Soon light when it is idling for any period of time once the engine is warm. SES light turns back off once engine goes above idle for 5-10 seconds. It's sending error code 35 - "Idle Air Control System". The truck runs fine both at idle and above. I replaced the idle air control valve and there is no change - SES light still comes on....any ideas?