2004 F-150 XLT 5.4 with 50,000 miles. A few weeks ago, I was out and about. The truck had been running fine all day. I was headed home and all of a sudden I come to a stop light and notice a miss. Sitting at the stop light, the RPM would drop a bit and the truck would shake, then back to normal idle. It would cycle this routine about every 3 seconds. While in motion, I don't notice the miss. It's only when the truck is sitting still, whether in park, neutral, or drive. I haven't driven the truck since due to being out of town for work and just being busy with other things.

In December, I had the plugs and fuel filter replaced. A couple non-stealership mechanics have told me that there is a TSB for a rough idle and there have been 8 or 9 updates to the code since I bought my truck, which was November of 2003. They said that they believe updating the code will resolve the problem. But I'm not so sure. What do you think it could be? Any help to figure this out would be much appreciated.

 

You'll want to start by checking whether your vehicle is throwing codes. My understanding is that most auto parts stores will do this for free. Once you have the code(s), you can look them up here. You'll have much more guidance and a better starting point if you go that route.

Good luck!

 

Will it throw codes even if the CEL isn't on?

 

I have had this EXACT same problem. I could never reproduce it at will though. The truck just did it whenever it wanted to. No codes were ever thrown.

To fix it (I just did this about two weeks ago) I removed the coil from each plug and put dielectric grease inside the boot and then reassembled. I also disconnected each coil and put a very small amount on both contacts at each connector. The problem has gone away. Now I can't say that it was indeed the addition of the dielectric grease but it certainly seems so. It could, however, be just a matter of re-seating all of the coils. I'll never know but at least it is fixed.

Just my two cents.

 

Was it raining hard when this happened?

 

Nope. It was bone dry.

P.S. Go Bucks!

 

Wet or dry didn't matter for my truck either way when I was experiencing this. Give the dielectric grease a try like I did. It'll only take you about 15 or 20 minutes...as long as the engine is cool. If it's hot then the two rear plugs on the passenger side are going to give you fits. It's tight back there and stuff gets hot.

 

Had a chance to work on the truck a bit this weekend.

It's not throwing any codes. I cleaned the MAF and Throttle Body. It seemed to be a bit better afterwards, but would "hiccup" about every 30 seconds, instead of every 3 seconds.

I'm wondering if it'll take a few days of driving for all of the sensors to "relearn" the air/fuel ratio needed now that everything is clean. I haven't driven it in about a month because I didn't want to harm anything internally. I'm driving it to work this week to see how it does and if it gets any better.

I have an appointment next week to have the PCM updated. I'm not sure if I should proceed with that if the truck returns back to normal idle conditions. Opinions on that?

 

Does it do it only with the A/C running? Mine does what you're describing as far as the "cycling" of the miss/vibration only with the A/C on. If the A/C is off, it idles as smooth as it can be. Mine just started doing it out of the blue. Never had an issue before. 75K miles now.