stang wont hold idle level

[sgt.scared]

Ok i got stock 5.0 bottom, e-303 cam tfs tw 170 heads that has been ported to about 185 i think. cold air intake, 70mm tb and 70 mm egr , tfs street heat intake , 76 mm mass air with 24 lbs sample tube and 24 lbs injectors , bbk long tube 1 5/8 headers . new o2 sensors.....
runs good down the road . smell gas at times , hold hand over the pipe some black sloot is there , not much.
it idle form 500 to 1500. up and down over and over. I can make it idle smooth by turn the tb screw up till it on 1500 then it idle evenly.

WHY wont my car idle right ????? Come on some one know this answer...
fuel presure reg ? mass air ? injectors ? fuel pump ? IAC IAB vavle ????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????
And there is NO VAC LEAK.

 

[jrichker]

See the "Surging Idle Checklist for help with all your idle/stall problems.

The quick and easy way to dump the codes is in there too, and all you need to do it is a paper clip! The first two posts contain all the updates to the fixes. At last count there were 24 possible causes and fixes for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.

 

[Mustang5L5]

Please...run the codes. Gives you a good starting point because anything else is just guessing

 

[90fox306]

I wud bet you that its your IAC!!! Had the same prob!!! Unplug it ( it will run like poo ) and if it idles dwn thats it. You can clean them if there not to bad.