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V1212
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May 29, 2023, 11:58 AM
Post #1 of 14
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99 F150 Rough/low idle!
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I have a 99 Ford f150, 4.2L with 201400 miles. The engine runs very low at idle and sometimes stalls when put in gear. However, if I rev the engine to 2500rpm it will run just fine for about 5-10 min like new. While driving, or idling for too long, the power will drop and it acts like it isn't getting air (i.e. if I blow air into the breather the engine will run just fine for another few minutes) I have changed the MAS, IAC, new plugs and wires, both "down stream" O2 sensors and reset the ECM, cleaned the throttal body and EGR valve. The problems started after resetting the ECM. It seems like something may be sticking and letting go after revving.
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Hammer Time
Ultimate Carjunky
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May 29, 2023, 12:26 PM
Post #2 of 14
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Re: 99 F150 Rough/low idle!
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Sounds like you wasted a lot of money by throwing parts at the problem.
First eliminate all vacuum or air leaks in the system (very important)
. You may have a bad IAC ( idle air control) but try cleaning the throttle body first. Remove the intake snorkel, have someone hold the throttle wide open for you and scrub the back side of the throttle plate and surrounding bore with an old tooth brush and some carb cleaner. Be sure to spray some into the small holes next to the throttle plate. That should help stabilize the idle. If it still has a problem, replace the IAC.
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V1212
Novice
May 29, 2023, 2:07 PM
Post #3 of 14
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Re: 99 F150 Rough/low idle!
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I cleaned the throttle body again and checked all vacuum lines I could find. The IAC is new, should I replace it again in case this one was faulty?
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V1212
Novice
May 29, 2023, 2:12 PM
Post #4 of 14
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Re: 99 F150 Rough/low idle!
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It seems to have helped the idle some, but I'm not sure if it was the cleaning or just because it is at operating temp.
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Hammer Time
Ultimate Carjunky
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May 29, 2023, 2:13 PM
Post #5 of 14
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Re: 99 F150 Rough/low idle!
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I think I would first do a smoke test to make sure there are no leaks anywhere.
The idle is controlled by metering air through the IAC. If there is any unmetered air getting in anywhere it will conflict with the IAC. If you can rule everything else out, then I might try another IAC.
With the mileage you have the throttle body could be just worn out and leaky.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
(This post was edited by Hammer Time on May 29, 2023, 2:14 PM)
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V1212
Novice
May 29, 2023, 3:27 PM
Post #6 of 14
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Re: 99 F150 Rough/low idle!
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I did the smoke test and no vacuum leaks, so I went and got a code read again. I got the code P0122 for
Throttle/Pedal Position Sensor 'A' Circuit Low Input
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Hammer Time
Ultimate Carjunky
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May 29, 2023, 3:31 PM
Post #7 of 14
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Re: 99 F150 Rough/low idle!
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That's another indication that there could be a throttle body wear problem. If the throttle shafts have too much movement it can give you both problems.
You can monitor the TPS data with a scanner to see if it's jumping around.
The other thing we haven't touched base on is overall compression. That high mileage can bring out a lot of things.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
(This post was edited by Hammer Time on May 29, 2023, 3:32 PM)
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V1212
Novice
May 31, 2023, 8:08 AM
Post #8 of 14
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Re: 99 F150 Rough/low idle!
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Just as an update for other readers! Turns out my problem was 2-fold. Ones was that the TPS was getting old/worn and wasn't holding the idle steady. Second was that I apparently had one, maybe two of my spark plugs drop out (they only intermittently produced weak spark). So I replaced all plugs with Bosh platinum plugs, put on the new sensor and she was still a little rough and hesitated some (but not as bad). However, on my first outing I made it maybe 2 miles down the road with the vibration and she died. I started her back up and has ran fine ever since. I assume she had to burn off all the excess fuel/buildup. The fuel trim is still slightly off, but it's already getting better and she has her power back and now responds immediately when I press the gas and no feeling of dropping power while driving.
Thanks for the help and if there are no more replies from me, then the problem is solved.
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V1212
Novice
May 31, 2023, 8:29 AM
Post #10 of 14
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Re: 99 F150 Rough/low idle!
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I will make a note about the plugs, but the ones that were giving me the problem were Motorcraft. As for the throttle body, that is not an option for replacement at the moment. I called the Ford garage, Autozone, Napa, advance, O'reilys and checked rockauto. No one seems to have or be able to get one right now, neither new or rebuilt.
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Hammer Time
Ultimate Carjunky
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May 31, 2023, 8:37 AM
Post #11 of 14
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Re: 99 F150 Rough/low idle!
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Yes, I just did a quick search and they seem to be sold out everywhere. There are a few used ones on Ebay.
That is a big red flag that must be an ongoing issue with them causing them to be out of stock everywhere.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
Ultimate Carjunky
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May 31, 2023, 10:17 AM
Post #12 of 14
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Re: 99 F150 Rough/low idle!
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IDK but I'm finding asst. things cloned, hacked even with a brand name on them!
Look for typos in warning labels - strong clue it's a hack job part, Tom
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Hammer Time
Ultimate Carjunky
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May 31, 2023, 10:20 AM
Post #13 of 14
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Re: 99 F150 Rough/low idle!
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Tom, what are you talking about?
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Tom Greenleaf
Ultimate Carjunky
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May 31, 2023, 10:55 AM
Post #14 of 14
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Re: 99 F150 Rough/low idle!
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Hacked parts! They are everywhere. Name brands and all you can smell the errors sometimes it's a fake - this issue could be faked parts?
I have tons of them one in sight spells John Deere "Joen Deere" a good clue, Tom
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