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Discussion Starter · #1 ·
I am getting error code P0306 - misfire cylinder 6. My first suspect is the COP, but I've also read how a bad or dirty IAC valve could cause symtoms that can throw a misfire code. I'm sure the car is due a fuel treatment for the injectors, so that is a possibility as well.

I changed the plugs and upper and lower intake manifold gaskets about 2 1/2 years ago when we got it (my son's vehicle). It was idling horribly when cold started, but replacing the gaskets did the trick. Surely the gaskets haven't lost their seal already...right?

Any suggestions for what to do first in diagnosing? Which of the above should I start with?
 

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Without knowing any specifics as to the how and where of the car's use, my first look would be at what the code directs me to.Check the plug and COP of #6.If you have to buy a COP get the right one from the dealer with the VIN at hand.
 

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Discussion Starter · #3 ·
Thanks for your reply. This is just a daily driver for my son. It has been out-of-commission for over six months with a tranny issue, but now that is (hopefully) fixed. The code is just 'misfire cylinder #6', so could be COP, fuel injector, IAC valve. I don't really want to replace all those parts, so wondering what might be the best to start with.
 

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It might help to know what year & how many miles.

I would swap a couple of coils around, clear the code, then see if a new code follows the coil to the new cylinder.
Inspect the coils after you remove them: if they have any cracks, replace them. Something else you could check is the spring that's within the boot. I've seen photos of them when they've gotten really rusty. Here's a topic w photos of the spring removed... 2001-2004 V6 spark plugs+PCV without intake manifold removal

There's another topic w pics in the forums here somewhere that shows good alternative replacement coils, but I can't seem to find it.
 

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Discussion Starter · #5 ·
Sorry...it's a 2001 V6 with 145K miles on it. I ordered an OBDII scanner yesterday, so that will make it easier to check the codes once I get it. Changing COPs and going back to the parts store for multiple free scans was a little inefficient. I cleared the CEL two days ago by disconnecting the neg battery terminal, so am wondering if it will still be throwing a code even though the CEL is still cycling but not illuminated again yet. If it's not throwing a code due to the cycling, moving the COPs around won't help at this point.

I still have an old COP I replaced about a year ago, and just now noticed that the spring inside the boot is a little rusted, and the connector in the COP has some corrosion as well. Boy that would be an easy and cheap fix.
 

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Swapping a couple of coils around seems like a good idea to me - it's a basic & simple thing to do.
The dealer probably has special equipment to check them.
If the problem doesn't follow the coil, then check the spark plug.
The coil wires may need replacing - the car has a lot of miles.
If it's not the coil, spark plug, or wire, you could install a new intake gasket. Maybe not, since you replaced it recently(?).
Another possibility is a cracked intake manifold.
In the mean time you could check the fuel pressure & the fuel flow.
And check the fuel injector - there's probably a resistance value for it.
If it's overdue, replace the fuel filter.

From what others have reported the IAC often times does not throw a code, but maybe it is in your case(?).
If your car is idling poorly, then it may need to be cleaned or replaced.
 

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Discussion Starter · #7 ·
Thanks. I'll try moving coils around first, and inspecting the coil wires before buying new COPs since they are so expensive. I ordered an ElmScan which connects to a laptop via USB, so that should help diagnose whether moving the COPs around creates a pattern.

For cleaning an IAC, is SeaFoam safe for that? Just spray it up in there where the spring and rods are in the IAC? I'll probably clean the throttle body in general.
 

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Most folks remove the IAC & spray it with carb cleaner or something, but it's usually a temporary fix.
Removing it should be easy on your V6; be sure to install a new gasket afterwards.
Be sure to use a coating safe throttle body cleaner. Use a MAF cleaner on the MAF sensor if you decide to clean that as well (& don't touch it with your fingers or anything).
 

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jdjohn, it isnt safe for the TB...it will remove the coating unless seafoam came out with a TB cleaner...use a TB cleaner for the TB.

This sounds more like IAC valve going out but like somebody on here said it dosent usually toss a code. I had the same problem on my taurus (nearly the same DOHC as the escape, but the escape engine is slightly more sophisticated), but it ended up to be a combination of a failing fuel pump and a couple bad COPs. Long story short, the fuel rail wasnt getting enough pressure due to the failing fuel pump and it misfired intermittently on different cyls which ended up fouling 2 COPs. All that was replaced on it prevented it from leaving me stranded on the HWY (as it did before) but it still idled like a lawnmower and sounded like one too. No codes at all but the IAC valve was clicking loudly while idling. I dont recommend this but wacking the IAC helped it settle its idle a little. It was never replaced bec i traded it in.
anyway check the fuel rail pressure with a fuel pressure guage. theres a little shrader valve on the fuel rail where u can test it at.
 
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