1989 Ford windsor idle problem

I have a 1989 Ford F350 with a 351 Windsor. I had to replace the long block with a rebuilt one. I re-used most of the original parts with the exception of the distributor and water pump. When I start it it sounds fine, a little bit of a rough idle but not bad. It then seems to surge as if it had a long duration cam. When I tap the throttle it goes away for a minute or so. Any help would be greatly appreciated !!!!!! Also no check engine light on.

Check for vac leaks & clean the IAC Ford Fuel Injection » Idle Air Bypass (IAB) (http://fordfuelinjection.com/?p=39)

Thank you for your help. I replaced the IAC valve and its better but... not rite. still starts to surge after a bit. Its seams like a switch kicks in or out and changes the idle. definatly perplexed.

Thank you for your help. I replaced the IAC valve and its better but... not rite. Still starts to surge after a bit. Its seams like a switch kicks in or out and changes the idle. Definatly perplexed. Fast idle is great but not gonna pass NJ smog tester.