Semi-Rough Idle AFTER long drive

Fordguy100 · Nov 26, 2012

After a long drive at freeway speeds (over an hour) my excursion has a rough idle. All fluids are fine, temperatures are fine, FICM was just rebuilt by Ed (with proper voltage). Everything appears to be fine, except after a long drive on the freeway.

Basically I will pull off, and the truck will return to an idle. The engine then starts to idle semi-rough. Not enough to catch on an iphone mic, but enough that I can feel it (and see water in water bottles vibrating) and so could my wife. Almost feels like its loping and or it cuts out for 1/1000 of a second every second or something like that. Its not burning coolant, smoking white, etc. On short drives, it does not do this, only after a long drive.

When I get back onto the throttle, its perfectly fine. Acceleration, power, fuel economy, all are fine. Its not enough of a fluxuation to notice any difference on the factory tach, and I didnt change out to notice what it was on the CTS. First thing I'm going to do is to confirm all the wiring to the FICM is attached perfect, although I'm 99.99% sure it is. After that, thats where I need help.

After the last drive, it almost feels like it does it while driving as well. If I hold the throttle to where the rpm's are around 1200 in 1st gear (like 5mph) and I give it enough throttle to maintain rpm's but not enough to accelerate, it seems like it almost does it then as well. Went to the store after the drive, the Ex sat for about 20 minutes. Started up perfect, and ran normal for a couple minutes until the temps got back up to what they were on the freeway (just normal operating temps).

ICP, IPR, EGR perhaps? Wish my CTS could monitor more things.

Fordguy100 · Nov 26, 2012

It sounds exactly like this (listen to it when he is filming under the hood)

http://www.youtube.com/watch?v=xpPIJserIVk

sootie · Nov 27, 2012

SUB'D I'm having the identical problem with an 05 excursion and no one-i repeat-no one can resolve it. its the bosses truck and he is pissed that i can't get his truck fixed.

it runs fine but at an idle it has an intermittent miss. a little down on power and has a bit of a fuel knock.
interesting to hear what ppl have to say.

Atsah · Nov 27, 2012

I had a truck do this and it was the ICP sensor..

sootie · Nov 27, 2012

mine is brand new and if i unplug it-the problem doesn't change.

to the OP-i didnt mean to hijack, just figure we can both benefit.

Atsah · Nov 27, 2012

You guys still have your EGR systems intact?

sootie · Nov 27, 2012

mines deleted.
i also have new standpipes, injector feed lines, icp sensor & harness, fuel pressure regulator, new injectors (gb reman) all in the last 3k miles.

about 20k ago i did new alternator and batteries,

about 60k ago i did the egr delete, new ficm, hpop and a starter a bit before that

ficm voltage is great, fuel pressure is fine.
when i do the injector balance test it is not consistently the same injector causing the miss. i am seriously lost.

Fordguy100 · Nov 27, 2012

Yes the EGR is there. I'm planning on a EGR delete and oil cooler. Replace some sensors while I'm in there

Lassie · Nov 28, 2012

My 04 does this exact thing...only after interstate runs of twenty minutes or more. Truck idles rough after the long cruising speeds. If I shut it down for even a minute and then restart, it idles better. This all started recently and soon after, I lost the alternator....ended up changing batts, FICM, and think I also have a few dead inj's (see the "alternator kills 6.0's?" thread) If I ever get all that straight, I'll let you know if the idle gets better after long runs.

Lassie · Nov 28, 2012

And my EGR has been deleted for years. EOT and ECT stay within 6 or 8 degrees at highway speeds, so I don't think it's a symptom of a plugged oil cooler. During my latest batch of problems, I finally caught my FICM dropping below 45V and I've been watching it since the rough idle started. I finally caught it during Keying On.

Fordguy100 · Nov 28, 2012

So many possibilites!

FICM was rebuilt by Ed and holds steady at 48v.

sootie · Nov 28, 2012

hey-at least you have parts to replace! iv'e done them all and cant solve the issue

Lassie · Nov 30, 2012

Long story, but it may help. I talked to a local mechanic about this yesterday...He told me that Ford initially installed a throttle plate housing in the intake elbow, but didn't install the throttle plate. In mid 04', they decided to put em in and try to increase EGR flow. This throttle plate actually throttles the cold air from the intercooler. If it shuts down, more air comes through EGR and vice versa. The plate was not installed on the '05s and up, and a scoop was added to the up pipe to increase EGR flow. Ford abandoned the plate in a few short months. He recommended removal in any truck they're in.

Even though my EGR is deleted, this plate can still move and can choke down the intake air. The PCM controls the throttle plate actuator and could be closing it off on long runs trying to cool the combustion chamber. (Ford's reasoning for the EGR is to inject already burnt air into the combustion chamber, which retards combustion, which reduces cylinder temp and NOX emissions) He said my truck would act like a truck with a clogged EGR if the plate shuts down too far. He said this is typically not checked when EGRs are deleted because so few trucks have them.

I checked the truck when I got home, and sure enough, mine had it! I can't drive the truck right now to verify if helps, but it is now removed. If you want to check this, pull the cold side CAC tube off. If your truck has this plate, you will now be able to see it inside the elbow. Remove the four bolts on the intake elbow. The plate is slid into the rotating shaft and held on with two small screws (TORX heads). Rotate the plate closed against spring pressure and remove the screws. Keep the plate closed while removing to catch a screw if you drop one. After they're out, let the spring pressure rotate the plate up and simply slide it out. No more possible restriction. EVER!

sootie · Nov 30, 2012

Thanks for the info! i will check that when the truck gets back tonight. Would this plate be actuating at all rpms?

the thing is that mine does it even before a long drive.

Lassie · Nov 30, 2012

I asked the same question and he said he didn't know much about the throttle plate strategy. Maybe someone else will know when the PCM uses this plate the most. I would think it would be throttling the intake air down only when low power levels are requested (from your foot). Highway speeds are not very demanding unloaded and would be a good time to sneak burnt waste air into the intake.