Piston Slap: A Tribute to the Mariner's Idle Escape?

TTAC Commentator sundvl76 writes:

Sajeev,

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:

Sajeev,

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 sajeev@thetruthaboutcars.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.