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2001 Ford F-150 truck idles rough

Tiny
JOSHUA028
  • MEMBER
  • 2001 FORD F-150
  • V8
  • 4WD
  • AUTOMATIC
  • 14,000 MILES
My truck idles rough when I am in drive and foot on the break. Also when driving down the road at a cruise speed it kinda jerks or hesitates. I have a computer hooked up and no codes. I have changed out the IAC and IAT and changed the MAF but took that back because it didnt change anything. I have changed out the two big vacuum lines. I have not checked the little vacuum lines though. Also if it is related or a different issue. When I give it the gas for a fast take off the battery light comes on and goes off after it switches gears. I have checked the voltage from the alternator and it reads 13.8. Could this be the problem?
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Friday, July 23rd, 2010 AT 9:16 PM

18 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,724 POSTS
Check behind the throttle body. There is a vacuum hose that has a 90 degree bend in it. They are known to dry rot and cause a vacuum leak. Check that and let me know what you find.

Joe
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Friday, July 23rd, 2010 AT 9:38 PM
Tiny
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I have changed that one, is it long black hose that goes to a black thing on the fire wall with a green cap. Also there is small black hose about 6" long off the bottom of that black box. Also a little tiny plastic hose that comes off that and goes to the passenger side. I have not changed that line or any other little lines.
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Friday, July 23rd, 2010 AT 9:54 PM
Tiny
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  • MECHANIC
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I think vacuum is the problem. Check all of them closely and let me know the outcome.
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Saturday, July 24th, 2010 AT 1:17 AM
Tiny
JOSHUA028
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  • 13 POSTS
Ok I will do I use carb cleaner to spray on them?
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Saturday, July 24th, 2010 AT 9:44 AM
Tiny
JOSHUA028
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  • 13 POSTS
Well I took carb cleaner and sprayed every little vacuum line that I cooked see. I could not find a problem. The truck was running and did not change when I sprayed the line fittings. Could the alternator be messing things up it is is under voltage?

I see there is plenty of problems with this truck and engine size. Plenty of people are having the same issue.
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Saturday, July 24th, 2010 AT 1:16 PM
Tiny
JOSHUA028
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I am going to replace the egr valve to see if it is the problem. I took it off and sprayed the inside with carb cleaner and got some black stuff out of there. Hopefully this will tale care of the problem.
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Saturday, July 24th, 2010 AT 1:31 PM
Tiny
JOSHUA028
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  • 13 POSTS
I just replaced my egr valve and the pcv valve and still nothing. The rpms drop less but more often now when sitting still and in drive and foot on the brake. I did see the little black rubber hoses on my tiny vacuum lines looked dry rotted. But haven't changed them out yet.

I would like to say is that couple of months ago I did a tune up. I changed out my spark plugs so I had to take the driver side fuel rail off and the fuel injectors. Would that be a problem now?
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Saturday, July 24th, 2010 AT 5:21 PM
Tiny
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I would focus on the vacuum hose you mentioned. If you had done something wrong with the tune up, it would have started right away. Also, as far as the fuel injectors, do you smell any raw fuel? I want you to check one other thing. Since the tune up, make sure none of the plug wires may have moved and melted on something causing a miss.
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Saturday, July 24th, 2010 AT 11:01 PM
Tiny
JOSHUA028
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No I do not smell any fuel at all. When I reinstalled the fuel injectors I lubricated the oring before I installed them back in. Ok I will check those things. I saw on another blog that some one checked a valve on the EFI and it was dirty. Where would that be located? I could not find it in my chiltons manual.
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Saturday, July 24th, 2010 AT 11:08 PM
Tiny
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I'm not sure what valve they are talking about. Many times people will clean the MAF. I will check my manual to see if I can find anything about a valve.
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Sunday, July 25th, 2010 AT 12:26 AM
Tiny
JOSHUA028
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Well I did change out four short black rubber vacuum lines and my problem slowed down. Well from the start of my project my rpms were sitting at 900 rpms and now after all I have done it sits around 600 to 700 rpms. Now instead of dropping 5 rpms and back up it goes about 1 rpm to about half rpm drop. And when I am cruising speed it only acts up between 45mph to 60 mph. If I am sitting still at a drive through window and move up and stop it bogs down and back to normal.

I dont know if you have answered me before on this question or not but could it be an electric issue with the alternator? By the way nothing is showing any codes at all. I had a computer hookes up twice and nothing shows.
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Sunday, July 25th, 2010 AT 8:46 PM
Tiny
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The "no codes" is what is leading me to believe there is a problem with vacuum. As far as the alt, if the battery was run down very low, it could.
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Monday, July 26th, 2010 AT 1:48 AM
Tiny
JOSHUA028
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What shouldi do now? I can't think of anything else to do? Today when I was driving it seems like I have no problems at idle anymore but just between 50 to 60 mph range. It feels like the engine is bucking slightly. Maybe a different issue.
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Monday, July 26th, 2010 AT 6:36 AM
Tiny
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Have you checked fuel pump pressure?
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Monday, July 26th, 2010 AT 9:33 PM
Tiny
JOSHUA028
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  • 13 POSTS
No I haven't. I have thought about that. I can rent a thing from
Autozone I think.
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Monday, July 26th, 2010 AT 10:23 PM
Tiny
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Yes, they usually will lend them to you. You pay the cost of the tool and then they refund the money when it is returned.
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Tuesday, July 27th, 2010 AT 12:53 AM
Tiny
JOSHUA028
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Thanks for the help but I am done searching for the problem. I am going to take it to garage.
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Monday, August 2nd, 2010 AT 10:32 AM
Tiny
JOSHUA028
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If anyone that is reading this and have he same problem. I took my truck to the garage and it is an ignition coil that went bad not a vacuum problem.
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Tuesday, August 3rd, 2010 AT 11:38 AM

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