i was just playing with my old 91 and found the problem i think.
when i was tuning up the car(when i advanced the timing) i also changed the air filter.... i guess i was to rough with the airbox and pulled the rubber intake tube off the airboxe lid partially, which caused the sucking sound, it just did it again last night when i was playing with the car getting it ready to sell. so it wasnt actually directly related to the timing.

that might be a place for you to look and see what is wrong.