Chevy van, tr.code35. See if you can solve this 1

I have a 93 Chevy van with 97000 miles and a 5 liter engine. Recently the check engine light came on with trouble code 35: "Idle Air control system".
I replaced the valve, reset the computer and the same code comes on again (usually when pulling over and idling after driving on the highway). I am stumped. Can anyone figure out what the problem could be? I checked the vehicle speed sensor and it's fine. One possible clue is that the cruise control also stopped working. Also, the engine always surges for a while before idling at the proper speed (like when braking for a red light). These two clues may be completely unrelated. Any help is very much appreciated. Karo: m
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