[bummer]

someone please explain to me why this is. from cold start to full operating temp no issues runs/idles perfect with the vac leak, but when i stop the leak rough idle, sputters and bucks under light throttle.

idle with the leak is 700-800 rpm no fluctuation

without leak 400-500 with fluctuation anywhere from 1500 all the way down stalling

i lost my code reader but last time i pulled codes i remember something about the EGR

 

[mike85xlt]

bad injector maybe? i dont mess with much efi but a rich running condition is causing this which could be caused by a bad injector... or possibly your ecu is getting a bad signal from your o2 sensors... could be a plugged up cat??? idk im just throwin stuff out there... pull your spark plugs and take a look at em and see how their burning... if theyre gas fouled it will confirm a rich condition... make sure your egr tube isnt coked up....

 

[mike85xlt]

and where is the vaccum leak???

 

[wyoranch]

Yeah. Definitely running rich without the leak and the leak gives it enough air. Possible restriction in the intake also? Maybe bad clogged filter or a foam part of an old filter sucked into the intake tube...

 

[bummer]

intake has been taken off and cleaned, no cats true duel exhaust headers into glass packs. vacuum leak is upper intake top back hose(closest to cab) it runs into a t fitting at the t is a red pinkish hose i unhooked that hose. its dark out or i would post a pic.

 

[OJs?]

I would bet on a bad oxygen sensor. They will cause an EFI engine to fail smog...