if i close the screw more on the throttle body bringing in more air would that cause my speedo to be off because when i am going 40 i am really going 35mph

 

Adjusting the throttle has nothing to do with the speedo.
Your speedo is off for one of two reasons, 1-if you have white face guages then the needle was put on wrong. 2-If you or someone else did any programming to the pcm, the tire/gear setting are wrong because of the rear gearing or tire size.

 

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