4.0 flutters/almost dies upon start up - Mustang Evolution

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Old 06-28-2011, 04:18 PM   #1
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Join Date: May 2009
Posts: 58
4.0 flutters/almost dies upon start up

when i usually start up my truck, the motor will sometimes just die out. and if it doesnt basically everytime if its not warmed up it will sputter RPMS..go from 1200 to almost dying, to 1200 to 200...to 1200 to 400...to 1000 to 700 and then settle in where its supposed to...at this point when its sputtering the AFR is mad rich, after the AFR gauge goes through its turning on process (it goes from 16 to 10..just to warm up or something, just what it does...autometer gauge..)..it will go straight to 10 on the AFR gauge and when the RPMS start to get closer to being stable the AFR will get closer to 14.7...and then stay there when the RPMS stabilize..

also at this time when it is sputtering, the vacuum will get lower, when the rpm gets lower..so will the vacuum, that seems like a direct link (less revs, so less vacuum) but might be good information for helping??


i cleaned the MAF, that didnt help, im going to go out and check the IAC for carbon build up today..see what happens there..but other than that..i dont know

might be an O2 sensor? but i feel like if they were bad the check engine light would come on?

and if it helps, i can data log stuff on livewire (or whatever SCT software is)

----after i did some data logging with some random variables on the list..i see what once the open loop becomes closed loop, just about RIGHT after that, the RPMs will settle into its steady state. If that gives any more insight
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