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Low RPM misfire or stutter.. HELP!

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Old 10-11-2013, 08:43 PM   #1
Join Date: Dec 2012
Vehicle: 02 Mustang GT
Location: Alabama
Posts: 14
Default Low RPM misfire or stutter.. HELP!

Ok lets see if I can actually get an answer to this. Hours on google pulled up many, many people having this exact issue but never saying "oh well it ended up being a squirrel shoved up the tail pipe eatin a couple nuts!" Yeah at this point I got to laugh just to keep from going WOT with a hammer, bat, and cliff after I get tired!

Low RPM skip under any acceleration! Not seemingly missing at idle but maybe a slight one. I can throw it in 4th-5th and go up a hill and floor it and just past 1800 it goes from missing back to back to full power with no misses and smooths out perfectly!. Heres whats been done!

Changed MAF
Changed TPS
Changed IAC
Checked all plugs (only 8k on them, lightly white perfect gap)
I have swapped 2 new coils all around (only 8k on current ones. I even ran multimeter tests on them and the bad ones I pulled off, with the multimeter they all tested the SAME even the bad ones that I know were causing a constant miss and throwing codes!)
Cleaned MAF
Cleaned throttle body
Cleaned intake plenum
Checked for vacuum leaks
Made it skip like a school girl singing kum ba yah for 3 days to try and throw a code... Nothing!
No codes!
I have reset KAM
I have retuned to stock
I have retuned for full mods
Had alternator tested 13.9-14.2
Bought NEW battery
Ran 2 tanks of 93 through it
Checked wiring harness around all COPS and Injectors
At idle pulled wiring harness off COPS and injectors one at a time. (car stumbled each time)
Coolant lvl is stable

Im at a loss. All this happened after I put seafoam in the tank. It wasnt doing this a week ago. Everything in me wants to say o2s or COPS. But after the many many hours of research I see that if its either of those it would throw a code. And last time 2 cops went bad from me washing the motor.. yeah I know. I replaced them all but it was still a constant skip, not just under 1800. The only codes I have is P1000 (new to me but is incomplete drive cycle) and the infamous EVAP p0455. I did not change the plugs. The almost look brand new and are gapped perfect. They are motorcraft plats. The tips are very lightly white no cracks or liquid or even residue from liquid being there.

Someone want to give me some kind of an idea to do next?!?! I have had a header gasket leak on the passenger side since Ive had the car (a year) and dont know if this could cause it. I know the AC drain plug is over the passenger o2 but Im sure it would throw a bank code. My only idea next is an innovate wideband and data logger. I cant find a shop to hook it up to a diagnostic computer without them charging me 100$. I dont want to pay someone 100$ to go "well she looks good here!" Or tell me something Id kick myself in the *** for not already checking.

Someone give me something!?!?!

EDIT:02 mustang GT
If you couldnt look < to the left under my name. But hey.
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Last edited by SecludedGT; 10-11-2013 at 08:47 PM.
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Old 10-12-2013, 09:32 AM   #2
Join Date: Dec 2012
Vehicle: 02 Mustang GT
Location: Alabama
Posts: 14

So 150 views and no help?? Blah. Ill take it to ford I guess.
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Old 10-12-2013, 02:40 PM   #3
Join Date: Dec 2012
Vehicle: 02 Mustang GT
Location: Alabama
Posts: 14

Nvm This can be locked. Even though those plugs were almost new and looked new, I seen some people saying motorcraft plats would cause a skip even if the look good and are kinda new. So I put some Autolite 764s in it gapped them at .05 instead of .054 and shes not missin a beat!

Last edited by SecludedGT; 10-12-2013 at 02:51 PM.
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Old 10-15-2013, 07:17 AM   #4
4th Gear Member
Join Date: Nov 2006
Vehicle: '98 3.8L Mustang Convertible
Location: CA
Posts: 1,580

18 hrs is not enough time to give people to answer your question. Yeah, you got a bunch of views, but those people didn’t know the answer. You posted on a holiday weekend. People are out doing stuff… Have patience… Posting your frustration about the lack of replies does not make people want to help you more. You often get the exact opposite result.
'98 3.8L Convertible (Red w/ White top)

Last edited by petrock; 10-15-2013 at 07:20 AM.
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Old 10-15-2013, 07:17 AM
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