Hi Folks, I have a 99 F-150 5.4 with just over 100,000 miles. All of a sudden, literally overnight, this truck has gone from running perfect to running awful. When i start the truck it starts normally. Initially (for about the first 30 seconds or so) it idles properly. Then it will begin to miss. During this period you really have to baby the accelerator or the missing gets really bad. The truck hasn't died on me yet during this period. It just runs really bad. Eventually, after about 15 minutes of city driving it will clear up and run properly. The engine reaches operating temperature long before the idle problem stops. The truck will run fine from that point on until it cools off again. Then the cycle starts again.

I've been reading a lot about the IAC valve. Prior to this my truck used to surge sometimes when i would be sitting at a red light. I don't know if that has anything to do with this or not. Keep in mind that this miss continues throughout the acceleration range. I mean whether i'm on the interstate at 65 or the city street at 45 it will start missing if you accelerate too quickly. Even when you come to a stop at the red light the missing continues but the engine doesn't die. One final point, oddly enough the miss didn't stop after the 15 minute time period while i was on the interstate for a 250 mile trip. It continued throughout the entire length of the trip. By the way, the check engine light has not come on yet so I don't have any codes. It almost seems like the culprit is getting warm enough during city driving to start working properly but that during interstate driving it never gets hot enough to work correctly.

Any suggestions would be appreciated. Thanks.

 

Time to change the ol' spark plugs mine did the same thing and after a spark plug change she ran fine. Good luck and if it takes you a couple of hours that is normal there is a good set of how to directions in this thread that i used and it helped me out alot GOOD LUCK.



Jeremy

 

Thank you Jeremy, I'll give that a shot. I was hoping it would be some little sensor or something because i have been dreading changing the plugs. But oh well, time to get dirty

 

No prob bud but seriously print off them instructions by racerguy it will help alot oh and don't break off the little brass bolts holding on the coils!!!!


Jeremy

 

check to make shure that you don"t have a bad coil i have an 02 f-150 with the 4.6 v8 and it has around 99.000 miles on it i have already replaced 2 of the 8 coils i was told that around 100.000 miles that you should replace all the coils according to the dealer.i still have a studder in my truck whem i come to a stop but no hesitation at high speed . it only happens when i am at a stop light or idleing i suspect that i may have another coil going out but no light yet to let me know otherwize.any suggestions would help im pulling out my hair trying to troubleshoot this and im already bald. thanks charlie

 

...Welcome CJ to Ford Truck Enthusiasts!

See you on the boards. ….

 

Thanks guys for all your suggestions. I plan to give the plugs a try on sunday or monday. I'll let you know how it turns out. I'm sure glad this forum is here. Thanks to all of those who have replied to my post and to all of those who were involved in creating the guide for changing plugs.

 

Well, I want to thank both jjlogue3 and charlie jackman for their advice. You were both right. I changed the plugs and still had the miss. It turns out that coil number 4 was bad because of anti-freeze leaking from a hose above as mentioned by many people on this forum. The coil was changed and the leak was fixed. Now she runs like brand new. Thanks again for your advice.