TTAC Commentator sundvl76 writes:
Sajeev, reporting back:
You may be interested in this, if for no other reason than to add to your diagnostic toolbox; my experience certainly can’t be unique: Several comments below your post also suggested the motor mount(s) as the problem. I more recently discussed this with a professional wrench acquaintance, who also said that the mounts can be expected to go south after ~80K miles; he suggested using a padded floor jack to lift slightly on the engine during a time when I detected the “rough” idle (the oil pan on this vehicle, and maybe all Duratec engines, is waffled cast aluminum). Bingo! The vibration ceased when I did that.
I have now changed the large mount on the passenger side of the engine compartment, and can report that the vibration is no longer present. But, there is a bonus prize to this story: for the last 25 – 30K miles, I’ve been also chasing a creaking noise which occurred – again more prominently during cold weather than hot – at any acceleration from a stop sign/light. I would have bet serious money that it was coming from the rear suspension, and in fact went so far as to replace 3 of the 4 control arms in the rear (they’re fairly cheap and easy to replace), with no success. Replaced the motor mount::creaking noise vanished like magic!
This vehicle is nothing great by any means – wife drives it 80% of the time and it suits her needs – and I don’t care that much for it, but these nagging issues really made me start to think about dumping it. Whole new attitude now – it will stay around for a while yet! Thanks for your help and thanks for reading this. I enjoy your posts greatly.
Excellent! Nice to see my initial armchair diagnosis was on the money. All it takes is a fractional difference in mount height from new to cause this problem. Maybe a millimeter, maybe less! No way can you eyeball this and know for sure.
I am totally diggin’ the padded floor jack on the oil pan trick. Perhaps the pan needs reinforcement to work here, not just the old school sheet metal affairs. But perhaps all it takes is a little lift at one corner (i.e. not the big flat part of the pan) to prove the bad idle is indeed an engine mount vibration. Or put a long board on the jack so the weight is spread across the entire pan, from corner to corner.
No matter, glad to see you are now enjoying your ride much more. It’s hard not to love it after getting your hands, arms, legs and even your mind “dirty” in a successful diagnosis of a seemingly impossible problem!
Then Rene writes:
Greetings! I enjoy your fine column and blog very much. Keep up the fine work! With regard to the poor idle that your reader was looking for help with on his 2005 Mariner, I thought I would chime in after much experience with the Ford/Mazda Duratec family of V-6’s, particularly the 2001-2007 Tributes and Escapes. In addition, a 2003 Tribute with 199,000 miles is my daily driver. I have found that the V-6 idle issue, after all the usual culprits have been considered and/or remedied without result, could be these two things—a failed DPFE sensor, or the intake seals are cooked.
These V6 engines have a manifold on top which is bolted to a plenum riser, which in turn is bolted to the engine. There are six seals where each component meets the other, and as one might expect, after 100K the six seals between the plenum and the engine have grown crispy from age and heat (in far worse condition than the six plenum to manifold seals, which might still appear pliable). The lower seals harden and begin to suck air in, and this condition reveals itself the most noticeably by a poor idle and a drop in fuel mileage. I have had excellent results by replacing all the intake seals (a complete intake gasket set is required) as well as all of the smaller vacuum hoses, cleaning the MAF sensor (using MAF sensor cleaner, not carb cleaner) and air flow meter; in most cases, showroom floor idle is restored.
These engines also seem to favor Motorcraft platinum spark plugs; I’ve tried other plugs in a pinch or on sale, but the Motorcrafts produce the smoothest idle and best fuel mileage for me. Of course, if the DPFE sensor hasn’t ever been changed, it’s a good idea. This component is also exposed to a great deal of operating heat. Mine clocked 140,000 miles before it failed, but I’ve seen them go earlier….and later. You never know with those. Finally, my last fleeting thought on the subject: two half inch vacuum tubes tee from the large air intake hose (just after the MAF sensor housing) and each one plugs into a grommet in the rear of each valve cover. These grommets deteriorate from heat and contact with oil and fail with time, resulting in a vacuum leak that starts slowly but soon gets worse. These should also be checked and replaced if they are soft and gummy.
I hope that this info helps someone.
Thank you for writing! I thought a failed DPFE throw a check engine light (CEL)…as that’s my expereince in my ’95 Mark VIII. And boy, was that a fun sensor to replace on the MN-12 chassis! But I digress…
Rene’s great assessment of the Duratec V6s is something every long-term car owner must consider: dried up gaskets and rubber vacuum lines that either go brittle or gummy. And not just the usual suspects you see with a quick look under the hood, there could be gaskets you wouldn’t even consider unless you have the proper service manual and/or information from your model specific forum. And if you own one of the millions of DOHC V6s shoehorned in a wrong wheel drive platform, well, I promise you that your eyeballs can’t find all the hidden gaskets and rubber bits.
Send your queries to sajeev@thetruthaboutcars.