rond951

Just came back from a spirited drive 6k 3rd 4th 5th 17 lb boost when coming to stop idle is loping 5-600 and a noticeable air sucking sound definitely coming from under the intake manifold around the area of the Idle Control Valve(recently replaced with OEM part) bringing the revs up the air sucking sound goes away 11-1200 rpm but engine doesn't feel as smooth as it should be. AFR is reading 18+ and goes to 22 during loping idle. All vacuum lines seem tight most are zip tied. Restart car and it stalls unless you give it throttle to keep it running. Intake Manifold gaskets recently replaced. 1400 miles since turbo upgrade, head gasket, wastegate, clutch, etc. etc. I do have a small exhaust manifold leak(SFR 321's being built). Prior to todays drive AFR 14.9 at idle low 12's under boost.

moalaska

pressure/vacuum test your engine you can get a 2" or whatever size abs cap and jb weld an air chuck into it just set your pressure regulator to like 10-20 psi. check all hose connections for a blown off hose or vacuum line. you can disable the idle valve per lindsey racings tps adjustment writeup and see if anything changes. you can unplug an injector and or a spark plug boot one at a time to see if its an individual fuel/spark issue.

moalaska

what mods on your car?

rond951

LR Super 48 dual port Max HP chips 3 bar fpr stock AFM and injectors new ICV intake & exhaust manifold gaskets head gasket Spec 2+ clutch Wideband AFR MBC Autometer boost gauge new plugs fuel filter

Car has run flawless up until today with multiple hard pulls without issue.

I definitely hear an audible vacuum sounding leak but a thorough check shows nothing. I'm familiar with idle problems associated with vacuum leaks.Would a vacuum leak cause bad AFR readings?

Thanks

mtnman82

Do you have a vacuum/boost gauge? You should be at ~18inHg of vacuum at idle when the car is warmed up. This is a good way to tell if you have a vacuum leak.

Yes a vacuum leak can cause bad AFR. I've developed the same issue after trying to put on a stealth MAF setup several weeks ago. Car was running great with ~18inHg of vacuum at idle and perfect AFR's (stock AFM/chips), then after changing stuff out rough idle & AFR's are off. Vacuum gauge was at ~11inHg, so I believe I have a vacuum leak somewhere. Haven't had the time to track it down yet...