Rough Idle/ Sputtering on '06 V8 Limited

[BootyDo]

Hello
Hopefully not too long of a thread here, but I just wanted to list everything. Apologize ahead of time if this is excessive

About a month ago, my company switched locations to about 1/2 mile from my current house. Given the heat, (didn't want to walk and show up all sweaty), I drove my 2006 V8 Limited Explorer to and from work INCLUDING a round trip at lunch. After a week or so, I noticed my truck would idle very rough on the return trip from lunch, but was otherwise okay. Considering I needed an oil change, I took it in and had that done. Then, after opening it up on the highway, the engine light came on. Since I did the oil change and had just filled the gas tank the same week this started, I added about 1/2 can of Seafoam to the gas. I then used my OBDII scanner and found found the engine misfire code, (8th cylinder). I cleared the code and it's never come back on. BUT, the symptoms are still there.

I have the day off so I decided to let it warm up for about 10 minutes in the driveway. Once it warmed up, the shaking began again. I notice if I accelerate, (in park), to 1,500rpm, the shaking subsides. THen continues until I reach 2,000 rpms. Once I let off the gas back to idle, the shaking is worse than before accelerating it.

So basically, it seems the shaking happens when the engine is not running cool. I have a 1/2 can of Seafom I'd love to run through the engine, but I can't figure out where the IAC line is on this model. And I also have some throttle body cleaner I'd like to put in the IAC valve, but it looks very tricky to remove.

Any thoughts on this, (bad gas?), or is there something I can try with my OBDII scanner? I'm not very tech savvy, but would like to see what I can accomplish on my day off. I'm scared to take it out on the highway incase this thing breaks down.

Any advice would be appreciated!

 

[arco777]

There may not be an IAC, what with the electronically controlled throttles that most of these newer motors use.

Usually shaking (physically noticeable with hood open) of the engine is due to a misfire. Isolate the cylinder if you can. May or may not be #8. Check for one spark plug that looks different from the others, or if you have access to an infrared temperature thermometer, point it at your manifolds and note which cylinder's exhaust temperature is lower than the others.

If you can narrow it down to one cylinder (and not a general, scattered misfire across multiple cylinders) then your diagnosis is much easier. Check that cylinder for a bad spark plug or coil (try swapping with another cylinder and see if problem moves). You can swap fuel injectors the same way to see if the problem follows the part. Never hurts to physically check for spark by cranking the engine (with fuel pump circuit disabled) with a spark plug connected into a coil and grounded at the electrode. Missing spark at one cylinder with a coil-on-plug setup usually indicates a failed coil. It is also possible to check that the cylinder in question is mechanically functional with a compression tester. Lets you know that there isn't a giant hole in a piston or valve (unlikely but it happens).

Good luck!

 

[BootyDo]

Thanks for the reply arco! The CEL actually resurfaced again last night and the scanner pointed again to the 8th cylinder misfire.

I've searched a million things online and it looks like it could be several possibilities - including the Throttle Position Sensor. I'm not too mechanically inclined, but I figure it may not be a bad idea to pick up a new one. However, I've also seen countless things mentioning if it's a coil, I could swap the coils with another on the engine and see if a code points to the new cylinder. That sounds like a great suggestion, but is there any how-to or anything I should know if I want to swap the coil on the 8th cylinder? I've read that you should replace them in pairs but not sure if that's engine specific.

 

[arco777]

Just check the #8 coil by connecting a plug into it and touching the tip to a ground (like the block or manifold) and crank over the engine with the fuel pump fuse disconnected. You'd see spark jumping across the plug's gap if the coil is functional.

Or you could swap coils around and see if the misfire moves with the coil.

There's really no reason to replace multiple coils at a time. Just change out the failed one.

I can't see any reason a throttle position sensor would cause a single cylinder to misfire. Usually a part that affects all cylinders equally can only cause them all to work or all to fail (random cylinders misfiring, not the same one over and over).

 

[BootyDo]

Just check the #8 coil by connecting a plug into it and touching the tip to a ground (like the block or manifold) and crank over the engine with the fuel pump fuse disconnected. You'd see spark jumping across the plug's gap if the coil is functional.

Or you could swap coils around and see if the misfire moves with the coil.

There's really no reason to replace multiple coils at a time. Just change out the failed one.

I can't see any reason a throttle position sensor would cause a single cylinder to misfire. Usually a part that affects all cylinders equally can only cause them all to work or all to fail (random cylinders misfiring, not the same one over and over).

You sir, just talked me out of dropping $70 tonight! I think I'm going to give the coil tests a try. Just got to find me a how-to on this engine, (never did this before and about to abuse Youtube!).

I'll post back with updates - thanks again!

 

[arco777]

Should be the same as all modern Modular motors. Unplug the coil's connector, remove the hold down bolt, yank the coil out.

 

[BootyDo]

Well...they say there's no such thing as a stupid question...until they met me.

What cylinder is the 8th cylinder: The one closest to the firewall near the passenger seat or the one closest to the firewall nearest the driver's seat?

 

[arco777]

Well...they say there's no such thing as a stupid question...until they met me.

What cylinder is the 8th cylinder: The one closest to the firewall near the passenger seat or the one closest to the firewall nearest the driver's seat?

Closest to firewall on driver's side.

 

[BootyDo]

Closest to firewall on driver's side.

TYVM! Giving this a try after work. CEL came on so I'm going to pull the code before and after the switch-up. If it's the same code after the switch, I'll clear the CEL and see if it comes back up again for sure as the 8th.

 

[BootyDo]

Hello,
So just posting a quick update that has me a little alarmed...

I swapped the coil from the 8th cylinder with the one in the 6th(?). Before doing so, my CEL registered a misfire in the 8th cylinder, (P0308), and an additional code: P2107. I haven't been able to find anything concrete on that code.

Anyhow, when I took the coil out from the 8th cylinder, the spring showed a bit of bright rust and the tip was clearly wet. It didn't appear to be a greaser and no odor. After hooking up the battery again, the CEL was cleared but the issue definitely remained as before, (rough idle after the engine runs 3 minutes or so and get progressively worse/more violent). I'm hoping to see if the CEL comes bag on and begging it says P0306 or something, but any thoughts on the water?

 

[arco777]

Water is probably from washing the engine, like with a pressure washer. It gets past the coil boots sometimes.

Oil or water in a plug well can cause problems but may not be the cause of your issues. Do dry it out though and clean any rust off the plug and coil tips.

See what codes come up... Process of elimination may be the way to go.

 

[BootyDo]

Hello,

So it's been over a week now since switching out the coils. Unfortunately, the same symptoms appear, but still no code being thrown.

Given the issue with the 8th coil having rust and that the original CEL pointed to a misfire on the 8th, would it be safe to just go ahead and replace that one, (now moved to the 2nd to last cylinder)?

Also, I should note two things: I've never washed the engine, but I don't run the car enough in the event of moisture in the air setting in. Additionally, the coil that I took out of the 8th cylinder had some green paint on it. Almost like it was "marked". Is that some sort of code for "reconditioned" or something?

 

[BootyDo]

UPDATE:
Just received an Accel Coil and threw it in the 6th(?) cylinder that contained the one I originally pulled from the 8th cylinder: Night and Day. Say it again: Night & Day!

I'm hoping that the new coil isn't just masking another issue that might be going on, but I couldn't be happier!!!!! Going to Seafoam and bath it in Techron next.

 

[filipows]

Water in plug well

While trying to track down the source of a miss fire I pulled a coil pack and found a puddle of water in the plug well. Lots of water not just damp

If the water didn't come past the coil boot where else might it come from?