2006 Ford F350 Question

I have a 2006 Ford F350 V10 gas motor. It has a standard transmission, and has 189,000 miles on it. I recently had the plugs changes, all 10 coils changed, and the fuel filter changed (three weeks ago/less than 2,000 miles ago). On Saturday an idle problem began. As long as you are driving, the motor is running fine, but when you stop at a light, it will not idle (I had to keep my foot on the accelerator to keep it running). After the truck sits overnight, it will idle when you start it and for a few minutes after that, but then it begins to stall again. Any advice you have would be very helpful.

Thank you.

When they changed the coils, did all the harness plug ends clip on tight ?
It is common for the plastic lock tabs to break with age and heat.

Has the throttle body been serviced recently?

No, haven’t serviced the throttle body recently.

The problem might be with the Idle Air Control valve.

Anytime the accelerator is released, the IAC valve controls the engine idle speed.

This is such a common problem on Fords, I don’t even attempt to try to clean the IAC valve.


I don’t think this engine has an IAC valve.

hmm … the engine should be purring like a kitten with all that work done it, yet it is misbehaving now. It’s hard to say if the work had anything to do with this symptom. If it did, it would be more likely an electrical connector didn’t get reconnected not securely connected or something simple like that. So a visual inspection of that kind of stuff is in order, focusing on anything the shop might have disconnected while doing the service.

Sometimes just disconnecting the battery can cause this problem, as the computer forgets the parameters it has learned. But since your problem didn’t start until 2,000 miles later, that’s not the likely cause.

Another idea, if the engine computer isn’t reading the coolant temperature correctly, this can be a symptom. Good idea to check on that.

About the only other thing left, since the engine is otherwise running fine, is something with the idle rpm management system. That’s done a lot of different ways these days, so you need to find out how that’s done on your vehicle. Idle rpm is affected by a lot of things, for example turning the steering wheel, or turning on the headlights. Does your truck us an IAC device? Or do you have a motorized throttle valve with fly by wire computer control from the accelerator pedal?

This truck is drive by wire . . . no IAC

We have tons of these in our fleet

This truck will throw a code for a sludged up throttle body, if you let it go too long. They usually throw this code by about 60K

You also have the infamous 3 valve triton. The one where you try to remove the mile long plugs, and they break off. Not a big deal to remove, if you have the Lisle removal tool

Another thing I’ve noticed . . . misfires are often caused by the spring inside the coil boot. They tend to “unravel” which causes a wicked misfire

I’ve seen many misfires on these engines which do NOT cause the check engine light to illuminate. But there tend to be fault codes. A mechanic will see which cylinder is the problem if he performs the “cylinder contribution” test. Only a high level scan tool with very up to date software will do this

A cheapo scanner, or a code reader will not do that test.

If I’m right . . . and the problem may very well be something else . . . have the mechanic look at the cylinder that “failed” the cylinder contribution test. More than likely, he’ll visually see the problem. It’ll be either the coil itself, the boot or the spring. I’m leaning towards the spring