First time in this forum so I apologize if this question has been posted before. I just purchased an 04 Navigator with 34,000 miles and it has a really rough idle that does not feel normal at all. I've taken it back to the dealer and to no surprise "there is nothing wrong with the car or its most likely normal". I have a hard time believing that is normal and been having a hard time figuring out what the problem is specially when the AC is on it runs really smooth. Any help or advice would be appreciated since this problem is driving me nuts.

 

I think check AIC valve . Its the Idle Air Intake valve.

 

thanks for the quick response Aldrine.....so once I locate the air intake valve what exactly am I looking for to figure out whether or not there is something wrong with it....thanks...

 

I have an 03 Nav. Your truck has several vacuum lines coming off the upper intake manifold. I would look them over very thoroughly to insure there are no leaks (this would cause a rough idle). The IAC valve is a factor - typically wont cause a rough idle per se, usually too low RPM idle and a stall. Check for vacuum leaks in all the PCV hoses (theres a lot of line in your trucks PCV system) as any leaks there will cause a rough idle.

Did the idle get rough after some maintenance was performed? Was it all of a sudden? Has it always been like that? Did it happen after you washed the engine with a hose (probably bad COP if it did)?

If the vacuum system turns up no leaks, probably your next move would be to get one new COP (about $50) and one cylinder at a time put the new COP in and see if your idle smooths out.

I assume the truck is not throwing any OBD2 codes???

 

Thanks Calviroman.....

Actually I purchased the Navi about 3 weeks ago and noticed the problem the following day. I took it in to the dealer a couple of days later and they told me it was normal. I have been skeptical ever since and took it in a second time but I was convinced that they didn't inspected. It has not thrown any codes nor has the engine light lit up. It's suppose to have a certified inspection and it looks like they washed the engine, luckily it has a warranty for the next 3 years. I really appreciate the advice and will inspect the lines and then get help with the COP if needed as soon as I can b/c I'm pretty determined to get it fixed. Thanks once again.......

 

This caught my eye as I had the same exact problem today in my 150. I took my truck in to get a bypass put on my heater core because mine was blowing coolant in the form of steam out of my defroster vents. I pulled out of the dealership and at the first light, my RPM's dropped below 500 and the truck started running real rough. Mr. Genious mechanic disconnected a vacumm line and didnt put it back on. Check your vaccum again, and if ford says thats not it, I dunno, I wouldnt believe it, because it sure as hell sounds like thats the problem to me.

 

Have the same problem like this, sometimes it would idle below 500rpm and power is delayed when you step on the accelerator and then after rpm goes up when accelerating and you remove your foot from the gas pedal, rpm will go down super low and sometimes would die, after a while it would go back to normal then it would be normal until i restart again.

IS it the vacum lines?

 

Couple areas to check. Have you replaced the fuel filter as it may have never been changed before? and you might try running some techron in it. Typically a vacuum leak will throw a code so it doesn't seem like that's the problem.