Iac Valve Issues At Higher Speed

MOXterra

Test Drive
I’ve tried searching for similar threads and have had no luck. My 04 has been throwing the P0505 code(Error in the IAC system). When I start it I have to give it a little action with the gas to keep it alive, which I expected.

I didn’t expect it to impact how my car runs at higher speeds however. When I’m at 45 and 60MPH the vehicle vibrates pretty hectically only when I keep a constant speed with the throttle. When I let off it stops. Any chance this is a common thing or am I experiencing yet another issue? Thanks in advanced for any insight!
 
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