Idle issues?

[gts440]

I have a 2000 3.8, stick. Sometimes it idles fine @ 800 rpm. Sometimes it idles @ 1500 & then after about 6-10 seconds idle slowly drops down to 600, misses & sometimes will die & other times will idle back up to 800 & be fine. Any ideas on where to start?

 

[wmburns]

First check the basics.

Is the battery fully charged? Are the battery cables clean, tight, and corrosion free?

Have the alternator tested for correct output and excessive AC ripple. Most autoparts stores will do it for free.

Check for vacuum leaks. Don't cut corners.

Check the ignition system.

Review the following posts.
Is your mustang stumbling, dieing at idle or idling rough? - Page 14 - Ford Mustang Forums

A high idle is sometimes caused by a bad/nosiy TPS. Recommend reviewing the basics before changing parts.

 

[gts440]

got evap code (vaccum leak small)

Have sprayed every vaccum hose & connection with starting fluid with the engine running & no change in idle speed. Traced the evap (green cap) all the way back to the fuel tank & found nothing. What is the best course of action at this point? Thanks, gts

 

[wmburns]

Check the gas cap. Check the filler neck for rust through. Check the rubber grommet where the filler neck goes into the filler neck for leaks.