my 99 4.6 does the same thing, but it's kind of odd. it only does it at night, if it does it during the day time then all i do is check cylinders 3 and 4 for antifreeze and check the coolant hose over cylinder 4 and try to see if it's loose and that fixes it during the day time. the same fix doesn't work at night though so i'm starting to think my truck is just afraid of the dark.... i'm going to check my passenger side plugs here soon and also trying to change my exhaust manifold so hopefully that's the problem with mine
lol, to funny about truck being afraid of the dark
All these vehicals with this issue, is each current with maintinance? Fuel filter, plugs, wires, filters, PCV?
When plug wires begin to break down, (especially as they heat up from driving) you will loose spark. Also on these vehicals, 97 & above, Ford gets more & more technical with each, (sensors wise), and something as simple as a dirty breather filter will or can **** um up side ah ways, (make um run chitty).
Oxygen sensors as well as they begin to reach their max life. If you have over 50 or 60,000 miles on the engine may be worth changing them out before they offer codes.
We all have become spoiled to some degree with the CEL invention. If no light on, we can go without doing maintinance, more time to drink beer on Saturdays,
And the ole saying if it aint broke, don;t fix er. Another saying is fix er before it breaks & leaves ya on the road side! lol
With no CEL on this is what I try to pay attention to as I drive.
Typically a vacuum leak will increase or kill your idle as well as make for some rough running engine when loaded.
Electrical, (plugs, sensors, wires, ect) will sputter under load, (as described in some above post), if from wear, it will begin gradual & become worst as the part becomes worst from wear.
Fuel filter, air filter, MAF, will cause rough idle, worst when loaded, & even more worst when increasing the load such as giving it more gas.
In addition, I review my records to see if it is time for any maintinance.
Hope this offers some help, if not, bac to drinking that beer
Ive been having same problems with my 2001 f150 V6. Finally after a year or longer I had a mechanic replacing gaskets etc.. on my motor. While he was at it he replaced my Throttle Posiotioner Sensor and did some other adjustments. Got my truck back and best it had ever been , no idling problems at all!! On way home my check engine light came on and I checked them and it was Cam Sensor problems. Talked to the mechanic and he had to put the adjustments back and now the rough idling is back...so I think/sure all the idling is due to a cam sensor problem etc.. Oh and I never had any codes until he made adjustments with the cam sensor
Last edited by austinsdad; 05-25-2012 at 02:08 PM.
Reason: forgot a line
You will have to check your spark plug and spark plug wires because these are the primary causes of rough idling. Also check timing belt and clogged filters because these are another common cause of rough idle.
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If you are in gear foot on the brake and you are feeling a rattle or vibration thats a motor mount maybe harmonic balancer. If engine is spitting sputtering and falling on its but thats fuel or spark. If your smog is clear I'd say its spark.
OK update for all of you, I had the same thing and took it to a garage i trust. They looked at it and found, of all things, the coil pack had water in. Still not sure how and they showed me, i work close by. cleaned it out and it runs like a charm. I haven't run it through anything or washed the engine. When I asked more the mechanic that found it said the if it is really humid this can happen. really weird but happy. good investment of 75 bucks for their time and they were more than happy to tell me.
My '10 4.6 2v does the exact same thing ! Primarily with the AC on, in Drive and foot on the brake. I think it's based mostly on RPM. I have been through every possible option, all hoses for leaks, changed plugs several times, cleaned TB,replaced MAF, cleaned injectors, even just replaced o2 upstream sensor due to CEL coming on at 142k. Here's what I have noticed... in park at warm idle, put foot on the brake, no change, the idle stays at about 600-650rpm. Put it in Drive with parking brake on securely, and let it hold on the Parking brake, foot off the brake pedal and it will probably stay at about the same RPM. Put your foot on the brake in Drive , and mine drops down to 500RPM or less ! I feel this is borderline RPM to keep up with all the demands on engine with AC on etc...have yet to check fuel pressure, but it's on the list to do. Will also be blocking off the vacuum line to booster to see if same thing happens, to prove/disprove a bad booster. My plugs seemed lean at last change, which makes me feel it's a leak somewhere, just have not found it yet. For what it's worth, mine did not start this until after about 53k miles, I bought it new in '11, and I put on between 40-50k a year on this thing , I know how intimately how smooth it was before and it's definitely different now and has been this way for a while, just trying to work my way through it. I know it's resurrecting the dead as far as this thread is concerned...but it's been a boring night
All this sounds familiar to me. I've a '97, Scab, 4.6, 2wd with (now) 234,000 miles. This is a California truck I've owned since new, so it has four cat converters on it.
rough idling started around 150,000 miles. I never found any mechanic (including Ford) that could help so I lived with it.
On a trip to Nevada last May headed for Carson City (from Oregon) I clearly noticed a lack of power on hills and when going over the last hill into Carson City the truck was really struggling and a check engine came on. Stopping at a shop the code showed "catalytic converter failure."
Changed all four Cats and O2's and I had a new truck.
Looking back it became apparent the Cats were in failure mod for a long time. Cats have a definite life, especially when you pour chemicals into your tank trying to figure out what's wrong.
This may not be your problem, but they sound familiar to me and are worth a check.
Last edited by j.low; 07-16-2014 at 11:59 PM.
Reason: missing words
I had a similar problem with my truck.. found out this morning I had some moister in the number 1 cylinder from a previous intake manifold leak that I replaced. dried it out now runs smooth... I know this is an old tread but thought it might help someone else searching this problem
i have similar issues with my 4.6, i think the cats are suspect but i have a different situation. i live in colorado springs, elevation is at 6600ft above sea level, normally i put 87 octane in it, thats when these problems that everyone talks about worsen especially when its above 80 degrees and the underhood temps are higher. now if i put 85 octane in its not nearly as bad, although 85 is not the recommended octane. now im not saying this is a fix or anything, just stating my observations with my truck and particular situation. ive been dealing with this issue but it bugs the crap outta me