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p1506 with intermittent stumble under 3k rpm

K

KAOS_3.0

Hard-core CEG'er
Joined
May 16, 2008
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SE / CLT,NC / ATL,GA
this issue comes and goes, and seems to get better if I dont run ethanol fuel. the stumble is only below 3k rpm, under load, and usually at more than half throttle. pretty much the fun part, lol.

the p1506 comes and goes. once the light triggers, it takes about two days to go out. I have tried using a crc product that is like seafoam in a can for gdi engines, spraying bursts of it onto the intake after the maf with the throttle closed until the engine almost stalls in order to wash out the IAC. I am not detecting a leak around the iac when I spray maf cleaner around it. also cleaned the MAF and swapped out the k&n in it for a the other clean one. (having two is nice for that, lol).

I did search, but only came up with three results, in which, basically everyone was having an o2 event of some kind or a misfire as well as the 1506. mine barely triggers the 1506, it just runs like crap half the time. and by half the time, it's not like I mean every other time I drive it, it's more ike every other time I roll off from a stop. very unpredictable.

anybody with suggestions would be worth a shot? thanks!

PS: for those who dont know, this is a 2005 full 3.0 with no cats, mil eliminators, and a tune...
 
Try pulling both intake manifolds, clean them, pull the AIC as well and clean it. Excess carbon buildup in the engine can cause this, as well as a host of other problems.
 
meh, if I have to pull the manifolds I'm going to put double iridium NGK plugs in it with new bosch wires while I'm at it, and I'd like to hold off on that since the plugs and wires arent that old. keep in mind, this is a full 3.0 with the plastic manifolds and unobstructed IAC ports and straight shot EGR inlet. not a lot of stuff to get plugged up besides the iac itself. I was hoping that the GDI aerosol can of seafoam type stuff would clear this up for me. I can hear the IAC breathing healthily from the end of the MAF when I was messing with it. I might hunt around the UIM and see if I'm missing a vac leak. dont get out till night time tonight and tomorrow though, so it'll have to wait till wednesday. hoping to get my emissions done thursday though. hopefully the code will clear up and I can get it passed emissions, then I wont haveas much to worry about, lol.
 
The IAT could cause it, but it can be caused by a host of other problems as well. I am a guy who suggests looking at everything, including simple stuff without buying parts first. Clogged intakes and vacuum leaks are the first thing I would check.

Plastic intakes also can cause issues like this; they crack easy with the hot/cold cycles. I have replaced numerous plastic intakes on a number of vehicles because they crack. The Ford 4.6 V8 and Toyota 3,0 liter V6 uses plastic intakes that are known to crack in various years.
 
never heard of a duratec manifold cracking. only thing that could be an issue would be if the uim worked itself loose against the hood. there is a slight bit of contact between the iac and the hood, hence why the iac area was the first area I checked around with the MAF cleaner...
 
I've noticed that if I run higher octane gas or add octane booster and run it in cold weather the issue is almost nonexistent.

it also occurred to me that this started after the fuel pump went bad and I replaced it with the one from the contour that I had in storage. can a fuel pump be intermittently weak? seems odd, but the contour had this issue too, and now that this car has that fuel pump, it's acting the same. this hadn't occurred to me until the other night when I was driving it around and it was behaving perfectly, that the contour used to do this occasionally too...

the contour wasnt throwing the IAC code though, and I had always attributed its issues to melted cats. which I solved by removing gutting all of the cats...
 
Bucking under load at low RPM's is classic ignition problems.

Not sure why you're even thinking about the IAC, since you aren't having trouble at idle.
 
because I have a code for iac overspeed, and absolutely zero codes for any misfires....

without any information from the obdII system, yes, I would immediately think either carbon tracing on the wire ends or burned out plugs that need replacing or a closer gap. are you saying the PCM has no idea what is goin on in the engine?
 
You can throw a lot of misfires before it sets a code. My Cougar was tearing itself apart with misfires for weeks while I threw parts at it, and it NEVER REGISTERED A CODE for misfires. Once I replaced the plugs and wires, it was miraculously healed.

Use your head, man.
 
ok, I got ya. just the last time it wanted plugs and wires was when there was carbon arching and it threw several misfire codes..

what is the part number for NGK double iridium plugs for this engine? I'm tired of replacing platinums and I'd like to be able to run race gas sometimes...

or if anyone could help me find out what ngk double iridiums to put in it. that would be great as well.
 
(Untitled)

Bringing this post back since I havent sorted this out yet and I need to get my emissions done this month because I got a fix it ticket for it...
 
I would lean towards plugs. And I would just use the single platinum Motorcraft SP433 or double plat Autolite APP104 plugs.
 
Do you have access to any diagnostic tools? Trying to figure these kinda of problems is usually pretty tough/impossible without some sort of tool with live/streaming data.

With a diag tool you would be able to actuate the IAC and make sure it isn't stuck or binding, and you would be able to watch live TPS values to make sure they aren't glitching or dropping out. As per misfires (if you even have any), you would be able to watch those happen live too.

Something tells me that the misfire isn't causing the IAC code, it's the other way around (if there even are misfires happening), so I would rule out fixing any ignition problems to fix that code.

It is possible that you have two unrelated problems, (high idle, misfiring) also.
 
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