Yesterday, after coming to a stop at a traffic light, my truck settled into a rough, rumbling idle that caused the truck to shake. Light turns green, apply throttle, truck accelerates and drives normal. Next light, same rough idle, but driving away, runs fine again. Third light, smooth idle returns and has run fine since. Never got any warning/check engine light. Was this a 'normal' fluke, or possibly a sign of something bigger brewing? Paranoia fueled by 2 years of flawless performance?
2008 5.4L
103k miles
TB and MAF cleaned at 100k
Gryphon installed last week (L2)

 

Any codes or check engine?.Could be a lot of things. Def not normal. Colils, plugs, filters and on and on

 

No codes or lights. Ran great ever since that episode. All filters, fluids, plugs, boots changed at 100k. Coils still stock originals.

 

Hmmm, don't know. I"ve had coils go bad on my other truck and it idles and runs horrible as you know but usually throws a code and keeps running bad. What about the FPcm under the spare tire. I think they cause a start problem but may do other things too. Mine was rusted and bad looking. Would'nt hurt to look if you feel like lowering the spare. They rust on the back side and cause issues. Sorry, that's all I got

 

Another thing I noticed, that could be nothing, is a very random higher fuel pressure reading. It normally runs at about 39psi (95% of the time). There are some occasions though, where it will be 49psi, or as high as 57 psi. Runs fine, but wondering if that's normal.

 

Might want to check the injectors

 

Id check the FPDM first since its fairly easy. Then maybe the coils since they weren't changed or the injectors.

 

I've heard that VCT solenoids can cause this from time to time......but..basics first

 

I was just about to follow up on this post. I replaced the FPDM, and still had the occasional rough idle. I decided to go out on a limb and try something. A few days prior to the idle issue, I installed a Gryphon Edge tuner, set to level 2, on my truck. Wanting to rule out the tuner as a potential cause, I set it back to 0/stock. A week of driving, with perfect idle followed. Hmmm. So, over the past 2 weeks, I have bounced back and forth between level 0 and 2. I've found that the random rough idle only occurs when I have the tuner set to level 2. I haven't tried it in 1 or 3, but thus far, it looks to be that the rough idle is somehow associated with the tuner. I'm leaving it in 0 now because I'm afraid of what could happen if the rough idle leads to a stall at a very inopportune time. Any ideas?

 

I get a hic-up every now and then also.. clears itself up.. been running level 2 on my Edge also.. maybe I'll spring for some premium and install level 3 again and see what happens.