2003 Mercury Mountaineer idle problem

[josh843]

I have a 2003 Mercury Mountaineer with the 4.6. After it warms up it feels like it has a miss or the engine shakes a little bit. It only has this problem at idle sometimes, never during acceleration or normal driving. I have recently changed the timing chain tensioners, intake manifold (dorman replacement), IAC (motorcraft), and the throttle positioning sensor. When i had the throttle body off i completely went through it and cleaned all of it. Wondering if anyone has had a seen this issue or if anyone has any advise on where to go from here.

 

[zpn_by]

Hi Josh - have you had the computer scanned? Even if your light isn't on there could be a code stored. This happened to me last year - the engine was running a little rough but still going, and I just let it go. Eventually I got a misfire code (turns out there was one stored as well which hadn't triggered the light yet) so I changed the coil-on-plug unit for the cylinder which was identified. Worked like a charm.

Scan your engine and see if there are codes stored. That would be the first step and can point you in the right direction. Given the age of your truck, I would guess you've got a COP going, which maybe hasn't fully failed yet. On the other hand, it might not be bad enough to diagnose yet... good luck, and please keep us posted.

 

[Explorer7813]

Check your MAF sensor

 

[josh843]

I have recently replaced all of the cop's, and changed the mass airflow sensor without any luck! I took it in to a shop where they did a compression test which came out good. They said there's something in the electrical system throwing the firing off! Anyone have any ideas?

 

[Number4]

http://www.explorerforum.com/forums/showthread.php?t=396533

Have you performed this procedure yet?

 

[josh843]

Finally figured it out! The timing chains were stretched and the timing chain tensioners were all gummed up and bad! When I first changed the timing chain tensioners I should've changed it all but I tried to go cheap and I paid for it! So in the end it wound up being the timing chains, timing chain tensioners, and broken timing chain guides.