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Discussion Starter #1
Kid #N reports that his car (170-ish K miles, and he's had it since 110K) is stalling on occasion. Most recently, this afternoon while he was having it checked for codes at the auto parts store (he was always the dramatic one of the bunch). Per the staff there, he has no codes (and has had no CEL), and the battery and alternator check out fine. It's stalling in Drive, and reverse, at low speeds. He reports that it runs fine at cruising speeds, highway speeds, accelerating/decelerating - all o' that. (He's 5 hours away these days, so I'm doing this remotely)

Background:

  • Plugs are Autolite's from back at 110K
  • Wires are Autolite from about 140K (damned squirrels!)
  • Coil is Motorcraft from January, 2019
  • Alternator was replaced by ASE master mechanic at 145K or so
  • Battery is new enough to have tested well this afternoon.
  • IAC replaced around 150K
  • Intake tuner valve gasket replaced around 115K
  • MAF cleaned 6 months ago, when air filter was replaced
  • Throttle body cleaned at same time
  • Fuel filter replaced at 110K
  • AC has been repaired/replaced seemingly countless times. I know this is the 3rd compressor.
My mind and gut are thinking along these lines:
1) Vacuum leak. Hey, it's a Taurus, right? They seem to have been born with [intercoursing] vacuum leaks. :mad:
2) Maybe the plugs are worn to the point where they're sucking-up lots of battery power to jump such a large gap. Maybe it causes the thing to stall, while not throwing any misfire codes. FWIW, we pulled the original plugs (color coded with paint dots) at 110K, and were amazed at how big the gaps were. It surprised us that it still ran, and didn't trigger the CEL. Still, with the new plugs, we didn't really notice a huge change in how it ran, so maybe I'm just [urinating] up a rope on this one.
3) IAC. Again, it's a Taurus.
4) Do the ,"Big 3". It's a rusty SOB, for sure. Were this the problem, though, I'd expect he see lots more symptoms.

He's looking to sell it soon, so he's hoping for a cheap repair. If my #2 idea was correct, he could smash down on the straps 'til the gaps were back in spec. He'd only be out the knuckle skin he'd leave under the hood as he wrassled with the rear bank plugs.

What sayeth the Peanut Gallery? Does something else spring to mind?

Thanks in advance,

FC
 

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Kid #N reports that his car (170-ish K miles, and he's had it since 110K) is stalling on occasion. Most recently, this afternoon while he was having it checked for codes at the auto parts store (he was always the dramatic one of the bunch). Per the staff there, he has no codes (and has had no CEL), and the battery and alternator check out fine. It's stalling in Drive, and reverse, at low speeds. He reports that it runs fine at cruising speeds, highway speeds, accelerating/decelerating - all o' that. (He's 5 hours away these days, so I'm doing this remotely)

Background:

  • Plugs are Autolite's from back at 110K
  • Wires are Autolite from about 140K (damned squirrels!)
  • Coil is Motorcraft from January, 2019
  • Alternator was replaced by ASE master mechanic at 145K or so
  • Battery is new enough to have tested well this afternoon.
  • IAC replaced around 150K
  • Intake tuner valve gasket replaced around 115K
  • MAF cleaned 6 months ago, when air filter was replaced
  • Throttle body cleaned at same time
  • Fuel filter replaced at 110K
  • AC has been repaired/replaced seemingly countless times. I know this is the 3rd compressor.
My mind and gut are thinking along these lines:
1) Vacuum leak. Hey, it's a Taurus, right? They seem to have been born with [intercoursing] vacuum leaks. :mad:
2) Maybe the plugs are worn to the point where they're sucking-up lots of battery power to jump such a large gap. Maybe it causes the thing to stall, while not throwing any misfire codes. FWIW, we pulled the original plugs (color coded with paint dots) at 110K, and were amazed at how big the gaps were. It surprised us that it still ran, and didn't trigger the CEL. Still, with the new plugs, we didn't really notice a huge change in how it ran, so maybe I'm just [urinating] up a rope on this one.
3) IAC. Again, it's a Taurus.
4) Do the ,"Big 3". It's a rusty SOB, for sure. Were this the problem, though, I'd expect he see lots more symptoms.

He's looking to sell it soon, so he's hoping for a cheap repair. If my #2 idea was correct, he could smash down on the straps 'til the gaps were back in spec. He'd only be out the knuckle skin he'd leave under the hood as he wrassled with the rear bank plugs.

What sayeth the Peanut Gallery? Does something else spring to mind?

Thanks in advance,

FC
I have had problems with stalling for the following reasons:
  • IAC (ONLY Motorcraft IAC worked well, aftermarkets ones were junk)
  • I replaced the crankshaft sensor, TPS, and reinforced the battery connections at the same time (one of these fixed it)
  • vacuum leak (PCV elbow)
 

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Kid #N reports that his car (170-ish K miles, and he's had it since 110K) is stalling on occasion. Most recently, this afternoon while he was having it checked for codes at the auto parts store (he was always the dramatic one of the bunch). Per the staff there, he has no codes (and has had no CEL), and the battery and alternator check out fine. It's stalling in Drive, and reverse, at low speeds. He reports that it runs fine at cruising speeds, highway speeds, accelerating/decelerating - all o' that. (He's 5 hours away these days, so I'm doing this remotely)

Background:

  • Plugs are Autolite's from back at 110K
  • Wires are Autolite from about 140K (damned squirrels!)
  • Coil is Motorcraft from January, 2019
  • Alternator was replaced by ASE master mechanic at 145K or so
  • Battery is new enough to have tested well this afternoon.
  • IAC replaced around 150K
  • Intake tuner valve gasket replaced around 115K
  • MAF cleaned 6 months ago, when air filter was replaced
  • Throttle body cleaned at same time
  • Fuel filter replaced at 110K
  • AC has been repaired/replaced seemingly countless times. I know this is the 3rd compressor.
My mind and gut are thinking along these lines:
1) Vacuum leak. Hey, it's a Taurus, right? They seem to have been born with [intercoursing] vacuum leaks. :mad:
2) Maybe the plugs are worn to the point where they're sucking-up lots of battery power to jump such a large gap. Maybe it causes the thing to stall, while not throwing any misfire codes. FWIW, we pulled the original plugs (color coded with paint dots) at 110K, and were amazed at how big the gaps were. It surprised us that it still ran, and didn't trigger the CEL. Still, with the new plugs, we didn't really notice a huge change in how it ran, so maybe I'm just [urinating] up a rope on this one.
3) IAC. Again, it's a Taurus.
4) Do the ,"Big 3". It's a rusty SOB, for sure. Were this the problem, though, I'd expect he see lots more symptoms.

He's looking to sell it soon, so he's hoping for a cheap repair. If my #2 idea was correct, he could smash down on the straps 'til the gaps were back in spec. He'd only be out the knuckle skin he'd leave under the hood as he wrassled with the rear bank plugs.

What sayeth the Peanut Gallery? Does something else spring to mind?

Thanks in advance,

FC
I have had/have 4 G-4 DOHC's. (3 '03's in my herd now, 5 drivers). I have had bad idle, all were PCV. Too slow, too fast, hunting idle. Never had IAC issue. In fact, got a JY one curded up and cleaned it. Switched it out and made no difference, OE and OE JY cleaned and oiled all the same, no issue. If the IAC has gunk it it, 99% chance PCV caused that. Pic of bad PCV issue.
Just my experience.
-chart-
 

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Discussion Starter #4
This is a Vulcan, rather than a DOHC, if that makes a difference.

The PCV is one thing we've not messed with, mainly 'cause it's the fancy "heater" kind that's $36 to replace, instead of $2.50. I seldom have heard of those going bad, but I can have him check it for vacuum leaks. Also, do those pop out like the cheap/normal ones, so he can shake it & listen for a rattle?

Thanks,

FC
 

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Quick test of PCV. Hot idling in "N". Remove the fresh air hose from the accordion. ( it goes from the accordion to the valve cover). Put your finger over the hose and feel for a vaccum. Feel vacuum in few seconds and the PCV is working.
If the engine gets upset when the hose if removed, put a finger over the hole in the accordion.
Last one I did, air is moving out of the hose, not it. New PCV and surging idle fixed.
-chart-
 

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Discussion Starter #6
Quick test of PCV. Hot idling in "N". Remove the fresh air hose from the accordion. ( it goes from the accordion to the valve cover). Put your finger over the hose and feel for a vaccum. Feel vacuum in few seconds and the PCV is working.
If the engine gets upset when the hose if removed, put a finger over the hole in the accordion.
Last one I did, air is moving out of the hose, not it.

Perhaps I'm not understanding your method.

Shouldn't the air be moving FROM the PCV valve, back INTO the air intake (accordion) hose? Positive Crankcase Ventilation should be sending excess gasses/pressure (from combustion blow-by) out of the crankcase. The PCV hose (more like a pipe, in this particular engine's case) would then send those gasses to the intake hose, to be burned again.

If I remove the connection between the PCV hose/pipe and the air intake hose (accordion), I'd expect positive pressure on the PCV side, and vacuum from the intake, would I not?

Thanks,

FC
 

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Discussion Starter #7
To be technical, on this car the other end of the PCV pipe connects to the hard plastic of the intake manifold, downstream of the accordion. It attaches just downstream of the IAC.

I'm sure this makes no difference to what you were explaining, but I figured I'd put all the info out there, just in case.

Thanks for bearing with me.
 

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On my 2006 there is a runner control valve that has been known to leak. I replace the gasket in my valve but it wasn't leaking. You may want to look at that and maybe use some electrical tape to seal the joint. I also agree with you about the PCV valve on the Vulcan being reliable. I never had one go bad on any of my Taurus and I logged over a million miles on four of them. I have always cleaned them with carb cleaner.

Also if the IAC valve is not OEM then that could always be a suspect.
 

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Discussion Starter #9
On my 2006 there is a runner control valve that has been known to leak. I replace the gasket in my valve but it wasn't leaking. You may want to look at that and maybe use some electrical tape to seal the joint.
Thanks for that. We replaced that gasket within the 1st 5K miles he owned the car. It was one of the first repair tips we got here, and worked like a charm. I mistakenly called it the "intake tuner valve" in my original message.

FC
 

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Discussion Starter #10
UPDATE:

He sent a video that showed the engine bay, with the motor surging noticeably at idle. Then he turned on the AC, and the video showed the tachometer swinging wildly from 500 rpm to 1500 rpm.

He removed the NAPA IAC he’d installed in 2016, and replaced it with the original Motorcraft one that he had hung onto for some reason. Voilà - a steady 850-ish rpms both with AC, and without.

In this particular instance, his packrat proclivity seems to have paid off. I think he retained the original IAC in case it was not the reason for his engine malfunction back then. That did turn out to be the case: ‘twas a disintegrating AC clutch that shorted out a fuse for the keep alive memory.

In any case, he’s got it running at no extra expense, and with nary a nick or cut on his hands. He’s crossing his fingers that this fix gets him through, and doesn’t turn into one of those famous, “well, it ran well for 3 days, but then...” repairs that Taurus are known for.

Thanks to everyone for the input,

FC
 

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I have/had 4 G-4's all DOHC. I got a JY OE unit sludged up and cleaned it. Switch it out with one car and makes no difference, all working fine. Point is, I would rather have a JY OE unit cleaned and than anyone's new unit. There is not much to go wrong. Just dirty.
And, most important. If it is not clean, highly likely the PCV is at fault. Proper working PCV means, nothing but clean, filtered air passes through it. Non working PCV and crankcase sludge can be pushed back up the fresh air inlet to the accordion and sucked through the IAC.
-chart-
 
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