The motor fluctuates from about 700-800 rpm for about 20 seconds then drops down to 500rpm for a second. It is also slow to come back to idle if you rev it.

What could it be? Iac motor?

Thanks in advance!

IAC or a vacume leak,

IAC would be my guess.

You had the intakes off right ?
Are all 3 vac lines connected back up at the rear of the
intake?.. pcv hose too ?, or check the plenum o rings to make shure they're still in the proper position/groove in the lower intake runners.