My friends mustang after the install of the throttle body and plenium was way out of wack. The car seems to jump from 400 to 600 after start up. It idles really low and sounds like it is just about to die. But if you give it a little gas and let off the throttle it stays at 2000 rpm for about 30 sec or so, then drops back to idleing funny again. It sounds cool when idleing because it sounds like it could be cammed, but everytime we are at a stop after giving it gas it goes back up to 2000 rpm and it sounds like he is just holding the throttle at 2000. I have checked every thing around the throttle body and plenium and also put the stock one back on but no luck. His odometer also shuts off randomly when he is driving and the speedometer will just go to zero at the same time but every other gauge still works. I have no clue what is wrong with the idle problem or his guages. Any suggestions?

 

Doule check all your vacum lines and electrical conection incase you took something off. Then if you still have problems disconect the battery. Then remove you IAC and look for dirt. If dirty get some carb, or brake cleaner and spray it down. Then re install IAC and hook up the battery. Start car and check for idle drop off and raise. If it still idles rough adjust the TB to see if it will fix it. Also you might have to recheck for leaks around the TB. You could judt have a leak. Good luck

 

The base idle is set too low and it is "hunting". You just need to nudge the idle set screw up a tad and it should be fine.

 

yeah... i had the same problem.... just dink around with that screw till the idle rests @ about 800rpm

 

on the 2003 mustang were is the idle set screw?

 

its on the trottle body.