2007 3.0 Flucutating idle after plug/wire replacement

[zpn_by]

Hi everyone - hope you can help us out with some tips tonight beyond what I'm going to attempt tomorrow. It has not registered any codes at all after showing its rough idle.

A friend just got a 2007 3.0 stick RWD with 160,000 km on it (100,000 mi). He bought some plugs and wires and asked for me to show him how to install them, so he came over this afternoon and we did it. However, after doing the change, the truck will run OK on startup at 800rpm, then will idle down to about 700, but quickly will start to fluctuate from 550-700. The plugs were Autolite Platinums and the wires were Prestolites. I would have preferred that he got Motorcraft plugs and wires, but everything seemed OK on the surface. It was Motorcraft parts in there before. I didn't check the gap of the old plugs, but the new plugs were installed with the gap at 0.051". The owner's manual spec'd 0.051-0.057", so I figured to go on the lower side to allow for wear in the future.

The old plug wires seemed OK (no damage showing on outside, don't yet know condition of core) but the plugs were pretty white, although not showing any real wear to speak of. I did tell him we could clean up the plugs and reuse them, but he wanted to install new for a fresh start. He had to take the truck home tonight, but he told me it was much stronger (could believe it as the wires looked original) but some of that could be the placebo effect

Tomorrow he is coming back over to trouble-shoot the idle problem. I checked the throttle body and found it was typically gummed up, not looking like it had ever been cleaned before. I told him to pick up an IAC gasket on his way over, and intend to give it a good cleaning. I also intend to check the resistance of the old wires and the new wires. Is anyone aware of a spec of Ohms/foot resistance for good wires? I'm wary of prestolite parts due to many reports of COP failure for their aftermarket COP for the 4.6, but I'm aware that many people run prestolite parts with no trouble.

Here's what I plan to check tomorrow, in order:
1. clean IAC and throttle body.
2. resistance of original wires and new wires
3. regap plugs from 0.051" to 0.054"
4. anything else you guys may suggest...

Thanks in advance - I'll check back in a little while and answer any other questions you guys have, if there is any more info needed to help me.

 

[zpn_by]

Bump? 28 views, no opinions or extra info to add? Even to advise if I'm on the right path, or if I'm missing something obvious....

Thanks guys!

 

[zpn_by]

OK. 35 views, 24 hours, no opinions? Thanks a bunch... We didn't get the chance to work on it this week, so will be next weekend. Any thoughts in the meantime, please drop a line.... if anyone has anything to add. Guess the explorer side is much more active after all.

 

[Runnin'OnEmpty]

...... the new plugs were installed with the gap at 0.051". The owner's manual spec'd 0.051-0.057", so I figured to go on the lower side to allow for wear in the future.

...... Is anyone aware of a spec of Ohms/foot resistance for good wires?

You have a good plan of attack spelled out. It's a good idea
to gap plugs on the narrow side to allow for future wear.

Plug wire resistance should be in the 6-12K per foot range.
Plugs themselves also have a resistance, measured from
the tower terminal to the tip. They vary from about 5K
to 10K ohms. Anything near this range is OK, since the
greatest spark resistance is at the plug gap itself....

I suspect you'll find the rolling idle cause will be in the
IAC or throttle body, possibly carbon build up.
Not much to add to your plan. Good luck and keep us
posted.

 

[C.A.Sizemore]

Trace the air line for the IAC. When I repaired the leak on my 4.0, the surge at cold idle got much better. I think I also need to do my IAC, but that has to wait, the hubbies VW just went to the shop.

 

[zpn_by]

Thanks folks. I'll be checking in with him tomorrow to see how it's running. Been cold as heck here this week, so I think he's going to have to live with it for a little longer. -25C isn't great for working on a truck unless absolutely necessary! Thinking later on about it, There is a good chance the PCM tailored its tune around bad wires and old plugs, and the junk in the intake, and just didn't know what to do with itself with the new plugs and wires, and the gunk in the system still present. I suppose I could have pulled the battery for a minute to default back to factory, but it likely still would have run rough.

I'll let you know how it's doing once I have a chance to check with him again.