Rough Idle
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Junior User
Joined: Oct 2005
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Rough Idle
I recently fixed my 99 f150 ext. cab 4x4, 4.6L.. Had an insufficient egr flow code..i replaced the egr valve and dpfe sensor thinking that was it, but my egr ports were completly stopped up.. my truck has 115,000 mi on it.. now, when i am in drive and stopped it will idle a little rough, sometimes are worse than others..it doesnt do it near as bad when it is in park or neutral.. i just recently replaced the plugs and wires...my gas mileage is also still down...i thought after fixing the egr problem that my mpg would go back up..maybe i am over dramatizing the situation, but if anybody has any comments lets here them...thanks...
Lead Driver
Joined: Jul 2003
Posts: 7,406
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From: Wheatland, Mo
You asked for it...and I am sure I won't be the only one to say this, so here it goes...IAC... Idle air Control valve. Located at the top/back of the intake manifold. A very well known failure when it comes to bad idles. Take it off, (2 bolts and 1 wire harness), using carb cleaner, spray it out really good allowing all the crap to drool out, then let it dry or use compressed air, (can or hose). Re-install and check your idle. If it helps, get a new one.(ABout $80 at the parts store). Cleaning will only last a short time before the problem returns. If it doesn't fix it, let us know and I am sure you will get other routes to take.
Elder User
Joined: Jun 2005
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I second What BillyBob69 said. but I would also check for any cracked or loose vaccum lines. You can use the same carb cleaner and spray around the vaccum lines while the trk is running it the idle goes up or changes any where you spray that is where a vaccum leak is.
Lance
Lance
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Joined: Sep 2000
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From: Flat Rock, Michigan
All of the above is solid advice, but i would also look at 2 other things.
1. Your fuel pump and fuel filter
2. Your fuel pressure regulator.
And with an intermitten rough idle, it is possible that your fuel pump could be failing. By the way, how old is your fuel filter?
With poor gas mileage, your fuel pressure regulator could be bad. Have you seen any black smoke coming from the tailpipe? Is the tailpipe caked with black soot? These are clues of too much unburned fuel being dumped into the engine. Sniff the oil on your dip stick.
Looks like you have some homework to do!!!
Keep everyone updated on your progress.
1. Your fuel pump and fuel filter
2. Your fuel pressure regulator.
And with an intermitten rough idle, it is possible that your fuel pump could be failing. By the way, how old is your fuel filter?
With poor gas mileage, your fuel pressure regulator could be bad. Have you seen any black smoke coming from the tailpipe? Is the tailpipe caked with black soot? These are clues of too much unburned fuel being dumped into the engine. Sniff the oil on your dip stick.
Looks like you have some homework to do!!!
Keep everyone updated on your progress.
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my fuel filter was replaced this summer..there is some soot in the tailpipe but nothing was caked on anywhere..i did notice some water in it though...not too sure if that is normal or not...i cleaned out the iac valve and i cant really tell that much of a difference..although there was some carbon build up in it...it doesnt miss bad or anything like that it's just not too smooth sometimes and i am the type that gets picky when things dont run exactly like they should..i did sniff the dipstick and it had a small fuel sent to it....i may have smelled it out of paranoia...haha...but it may not be a big deal...just may be old age...haha...thanks for the post guys...i really love this site...
Elder User
Joined: Jun 2005
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water is normal that is the cataletic converter doing it's job. Here is something to try it helped mine out alot. Get some Sea Foam for NAPA take the pcv valve hose off the pcv valve ans suck up 1/3 of the can while the trk is idleing. then shut the vehicle off for 15-20 min. then start it up and run it down the road untill the white smoke clears up (there will be what smoke to). that will clean your valves and piston chamber. it won't hurt your engine just clean it.
Lance
Lance
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i would agree with lance on the vacuum checks. i had a bad rubber grommet on my pcv line where it enters the back of the intake manifold. had a major crack in it. caused rough and irregular idle. gas mileage did not even exist! terrible. i put black hitemp rtv on it. it ran like a new motor. ford wanted to replace the entire pcv assembly at $50! check all vacuum lines thoroughly. it doesn't take much to create havock.
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Junior User
Joined: Oct 2005
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Hood...about that soot you were talking about...it would smoke alot on me last summer whenever i cranked it up..it did that for a few weeks and all of a sudden stopped...im not sure if that would have any correlation with you suggestions or not...
Senior User
Joined: Sep 2000
Posts: 385
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From: Flat Rock, Michigan
The black smoke i had was from a bad fuel pressure regulator.
Here are the symptoms i had when my fuel pressure regulator went bad.
- Very poor gas mileage.
- Heavy black smoke from tailpipe when accelerating.... or sitting at an idle and lightly revving the engine. The black smoke was visible from the side view mirror.
-The exhaust also smelled very rich (gassey).
Keep in mind that your IAC could still be bad eventhough you cleaned it. Did you use a new gasket?
Have you used anything in your gas tank to clean your fuel injectors or have you ever had them professionally cleaned? Good Luck!
Here are the symptoms i had when my fuel pressure regulator went bad.
- Very poor gas mileage.
- Heavy black smoke from tailpipe when accelerating.... or sitting at an idle and lightly revving the engine. The black smoke was visible from the side view mirror.
-The exhaust also smelled very rich (gassey).
Keep in mind that your IAC could still be bad eventhough you cleaned it. Did you use a new gasket?
Have you used anything in your gas tank to clean your fuel injectors or have you ever had them professionally cleaned? Good Luck!
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Junior User
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it may be my iac valve...i just hate to drop 60 bucks on something that could possibly not be messed up...i just put a can of seafoam in the gas tank yesterday...but that is all i have done as far a cleaning the injectors..that is really the only thing that i know to do to them...