Is the idle lower then 600 rpm? Does it seem like it's searching?

 

UPDATE !!!! Problem found finally after months. Previous owner installed the Intake gaskets wrong, in fact who ever did the work installed the old gaskets and put some kind of silicone on them and re-installed them. The other problem that was found was the #4 cylinder exhaust valve was slightly bent by the previous owners repair shop or who ever. We suspect while prying up the intake they used the #4 exhaust valve for leverage or something stupid like that. Thanks everybody for your help with this issue.

 

Glad to hear you got it fixed. Finding the problem and fixing it always puts a smile on my face.

No 1 reason I love to work on broken stuff.