By on March 5, 2014

TTAC Commentator sundvl76 writes:


Your post of 2 Mar 2011 was a great explanation regarding the cause of the “T” joint oil leak I’ve been experiencing. No one on any of the normal Ford sites has been able to pinpoint the problem, so I thank you for the information. (I’d discovered the source, but didn’t know the cause/fix until your post.) TTAC is now on my Favorites list!

So, I am hoping you might also be able to shed some light on the reason for the poor-quality idle I’m experiencing with the same engine. This does not seem to be a mis-fire, but more of a resonant vibration typical of an engine slightly out of time, and/or at the incorrect idle speed. It occurs primarily in colder weather (below 50F) and does improve once the engine is warmed – IF the ambient temp is above about 40F. When ambient is below that point, the strong vibrations do not disappear. Of course it is most pronounced in Drive/Reverse but noticeable in Park/Neutral as well. Manually increasing the idle speed slightly using the throttle does help. In warm weather the idle may be rough upon first start but improves pretty quickly.

I’ve investigated thoroughly (w/ propane) for a vacuum leak, cleaned the Mass Air Sensor and TB, and have replaced the IAC valve and spark plugs, with no improvement. There are no codes in storage to guide me to the solution, and I’m now thinking the MAS itself may be faulty but am not sure how to test it.

Have you seen this problem with other vehicles?

The vehicle in question is a 2005 Mariner with 114K miles.

Sajeev answers:

Thank you for your note, and Behold The Power of The Internet!!!

I often suspect the hydraulic filled engine mounts in these cases. A similar question was posted recently, and our commentators had suggestions you should consider. So have a read there, too.

sundvl76 replies:


Thanks for the link; read it all.

To add info to my question:

Engine mounts was one suggestion I’d found on another forum, and I’ve visually inspected them for leakage and also verified the engine does not move (power applied/brake on). Not saying it is impossible, but the symptoms are not the same as the Audi owner’s in the post.

Chevron or Exxon used 90% of the time, Shell occasionally. I also recall that when this first started (2 winters ago), I did an injector cleaning with the BBK kit, but no change in behavior was detected.

A small vacuum leak was also suggested – one which seals up when the engine is warm. Possible, but not sure how that matches up with my experience of the poor idle being dependent on ambient temps; the engine block should still eventually reach the same temp regardless of ambient. Incidentally, I’m in TX, so “cold ambient” is relative. . .

Thanks, I’ll keep watch on Piston Slap for further info.

Sajeev concludes:

If the engine mounts look that fantastic when running or not, consider the totally not impossible chance of clogged EGR passages.  I worked on a 1996 Sable LS (Duratec) that was EGR code free, but the uber-plenty EGR coking was a possible cause to its bad idle.  And while your Duratec V6 is significantly different from a UR-Duratec Sable, my EGR de-coking, fresh vacuum lines, a tune up (which you did) certainly cured the Sable.

And if those fail, perhaps you still need new mounts: perfection to your eyeballs doesn’t mean they are just out of spec enough to cause the funny idle.

Off to you, Best and Brightest.

Send your queries to [email protected]com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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13 Comments on “Piston Slap: A Tribute to the Mariner’s idle Escape?...”

  • avatar

    First of all Sajeev how is the 3 series holding up.
    Secondly I had a 89 Volvo 760 turbo that had a ruff idle and was informed that the transmission and the engine were not communicating well and had the mechanic to look at some of the electronics and parts that connect the two, the problem was solve…until the Turbo went then well I got rid of it.

  • avatar

    My last ditch solution has been to completely block the EGR, eliminating the possibility of problem. Works for me. But I don’t have to pass emissions where I live, either.

  • avatar

    If this is a 3.0 and i suspect it is, I would also check the DPFE sensor. One that is failing will often give you the same symptoms. Once it fails the car will not want to accelerate.

    It’s a cheap part from the dealership and takes about 5 minutes to replace.

  • avatar

    A rolling idle like you’re experiencing is almost always due to a vacuum leak (unmetered air), especially if it goes away when warm. The propane trick can work to find it, but be patient. Spraying throttle body cleaner can work too.

    • 0 avatar

      I’ve never had any luck with the propane/carb cleaner method, and found that a squirt bottle filled with water works very well. Its much safer and easier to use, as you can douse everything without having your face burned off.

  • avatar

    So I had the same problem on a Jeep GC. I did all the same steps that the OP did and had no luck. Gave up on it. Then my drive belt started squealing on full throttle upshifts because it was loose.. Replaced belt. Idle smooth as can be now.

  • avatar

    A Tribute to the Mariner’s Idle Escape

    Bravo – Mr. Mehta that title sounds like the beginning of a sequel to the “Rhyme of the Ancient Mariner”.

  • avatar

    How good is your scan tool? Can you monitor and graph the rpm to verify whether or not it is actually idling rough? What do the long and short fuel trims look like at idle? Are you monitoring fuel trims while searching for the vacuum leak? The fuel system will likely alter injector flow to compensate for the propane or carb cleaner before you will notice a surge in idle. Restricted egr passages will not cause a rough idle because egr is not commanded to flow at idle. A partially stuck open egr valve however can generate a rough idle, however the dpf (differential pressure feedback) egr sensor (unless it too is faulty, not at all uncommon) should notice the uncommanded egr flow and trigger a code. Do not block off the egr valve as a suggested solution. Its function is to lower combustion chamber temperature. This serves not only to reduce NOx emissions but also prevents engine damaging spark knock under load. The days of just pulling off all that useless smog control stuff are long gone. By the way, Motorcraft plugs only in this vehicle. None of that split fire or bargain basement Champion nonsense, and Autolite is not the same as Motorcraft. How did the coil boots look when you R&Rd the plugs? Any evidence of water (rust stains) intrusion? At that mileage I wouldn’t be surprised to see leaking lower intake gaskets but they would likely trigger lean O2 codes. Make sure the oil level is correct (too high and the crankshaft having to swim through any extra oil will cause rough idle issues). Also stick with 5W20, or 5W30 if you can’t get the 5W20. But first I would want to graph engine RPM to actually verify the rough idle complaint. Whats described sounds more like an NVH issue.

  • avatar

    Is this rough idle effected by humidity or just temperature? Is it worse when it rains? If so it could be a bad COP (Coil-on-Plug) coil. This was a common problem on the Escape/Mariner/Tribute V6s. I had a crack in one of mine on my 2006 Escape. It was worse when it rained. It was difficult to diagnose because it didn’t always throw a misfire code or it would throw a P0300 (random misfire)

    If it’s not any of these things there is one more thing you can try. If there are no codes or warning lights try disconnecting the battery for five minutes. It resets the computer and some say improves the idle.

  • avatar

    If the mounts are a known problem in the car, I would not hesitate to do it. S-classes have these issues, at around 60k regularly. Usually nothing wrong is visible until you place the old and new mounts next to each other on a bench.

  • avatar

    I agree with it being the motor mounts. Never saw hydraulic mounts last over 5-6 years, 60-70K miles.

  • avatar

    1, that title is a fitting tribute (pun intended) to all the such made on that platform, bravo. Two, I completely forgot the mariner existed until I saw a wierd light green colored on one the highway yesterday

  • avatar

    Hello all! I am a Mazda Master tech, and own a ’05 Tribute S myself. Here is what it CAN be and have repaired a few Tributes with the same complaint: Make sure you are using the manufacturer-supplied air filter!!!!
    Ive had several in the shop, compression equal, no codes, no ignition or injection issues, no vacuum leaks, etc.
    The factory airfilter has 2 strips of glue on the side facing the mass airflow sensor. The MAF only samples a portion of the intake airstream.
    The intake system, like the exhaust has pulses. A Filter without the stiffening glue can can react to the intake pulses at idle, cause a pulsing action itself that can confuse the MAF, and cause the idling issues.
    Another issue- a small “dip” wears into the camshafts just before the ramp the cam lobe. This dip allows the hydraulic lifters to pump up and cause momentary compression losses until the lifter bleeds down–and then repeats the cycle.
    Like the filter deal, I have repaired several of these also.


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