erratic/rough idle
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erratic/rough idle
recently my 85 F-150 300 I6 has been idling VERY rough. if the motor is cold, it will die at idle unless i keep my foot on the gas. once it gets warmed up, the idle remains rough but it will keep itself going, barely.
i took a look at the carb the other day and it appears as though the butterfly valve on the top of the carb(don't know its exact name, i'm an EFI guy) is not closing all the way at idle. if i manually close it while the truck is idling, it starts to run smoother. but it still doesn't run as smooth as what it did last week.
i have heard many bad things about the factory 1 bbl carb. could mine be on the way out? it has 166,000 miles on it with at least 1 rebuild on the carb which was performed about 10,000 miles ago.
David
85 F-150 300 I6 C4 3 speed auto
i took a look at the carb the other day and it appears as though the butterfly valve on the top of the carb(don't know its exact name, i'm an EFI guy) is not closing all the way at idle. if i manually close it while the truck is idling, it starts to run smoother. but it still doesn't run as smooth as what it did last week.
i have heard many bad things about the factory 1 bbl carb. could mine be on the way out? it has 166,000 miles on it with at least 1 rebuild on the carb which was performed about 10,000 miles ago.
David
85 F-150 300 I6 C4 3 speed auto
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Joined: Jul 1999
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erratic/rough idle
When the engine has reached operating temp the choke flap should be all the way open . If you close it when the engine is at O/T & it runs smoother this would indicate the engine is getting air from another source ...Vacuum or intake leak . It doesnt take much of a leak to cause a problem . Give the engine a close inspection before you condem the carb .
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erratic/rough idle
Hello. I have a 1985 that had the same exact problem. In my case it was the carb. But first like the others have mentioned check for a vacuum leak, your choke should be open when warmed up and about a third open when cold. Never all the way closed when cold. Also check your distributer cap, spark plugs and wires. If you have a digital multimeter your wires should measure 10,000 ohms per foot.It sounds like a vacuum leak to me, also check your egr valve for leaking. Greg.
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erratic/rough idle
well, i checked all of the vacuum hoses and can't find any of them that are leaking. the only place that remains to be checked is the intake manifold bolts.
now the truck is acting a little differant. when i turn the truck off(this only happens once it gets to O/T) it will do one of 3 things.
1. it will "diesel" and try to continue to run
2. it will "diesel" and when it stops it will let out a pop out of the exhaust
3. it will just pop out of the exhaust
so right now, unless all of this is caused by a bad seal between the intake manifold and the head, then something big is wrong. and to top it all off, for the next month i will not be able to work or drive the truck at all.
because of work, i will only be home for a total of 3 days this month after tomorrow. the things we do for money.......
David
85 F-150 300 I6 C4 3 speed auto
now the truck is acting a little differant. when i turn the truck off(this only happens once it gets to O/T) it will do one of 3 things.
1. it will "diesel" and try to continue to run
2. it will "diesel" and when it stops it will let out a pop out of the exhaust
3. it will just pop out of the exhaust
so right now, unless all of this is caused by a bad seal between the intake manifold and the head, then something big is wrong. and to top it all off, for the next month i will not be able to work or drive the truck at all.
because of work, i will only be home for a total of 3 days this month after tomorrow. the things we do for money.......David
85 F-150 300 I6 C4 3 speed auto
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erratic/rough idle
One thing you said about the carb. When you close the top butterfly the engine runs smoother, This indicates a vacuum leak. When you close the top your engine should die. Yours is getting too much air and closing the top cuts off some air and the engine runs better. One trick to find a leaking hose is take a pair of needle nose pliers, when the engine is running close off each hose one at a time. If you close a hose off and the engine runs smoother you just found a vacuum leak. You have a leak, you just have to find it. Greg.
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erratic/rough idle
thats what i had done to try to find the leak. i even got some carb cleaner and sprayed around the carb while the truck was running to see if one of the seals had gone bad, but the idle remained the same the whole time. thats why i think that it might be the bolts that hold the intake manifold to the head that might have worked loose. and it is very ikely that is the problem because the whole motor was replaced 9 months ago. if the bolts were not tightned properly then they could have worked themselves out by now. once i get back from work in about a month i will go back again and double check the hoses just to make sure though.
David
85 F-150 300 I6 C4 3 speed auto
David
85 F-150 300 I6 C4 3 speed auto
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erratic/rough idle
Re-torque the 4 bolts that hold the carb to the intake. Check your choke on the passenger side of the carb....this is where you can adjust the richness and leaness of the butterfly flap. Check to see if the air temperature sensors in the air cleaner are working properly....The preheat door in the air cleaner snorkle should be open on a warm/hot engine and stay in the closed position when the engine is cold. Is the pre-heat flexible tube in place coming from the exhaust manifold going up to the air cleaner snorkle?
Look for vacuumn leaks as the others have mentioned. Good Luck.
81 F-150
1 BBL carb 4.9L
187,000 happy miles
Look for vacuumn leaks as the others have mentioned. Good Luck.
81 F-150
1 BBL carb 4.9L
187,000 happy miles
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erratic/rough idle
[font size="1" color="#FF0000"]LAST EDITED ON 12-Oct-00 AT 02:03 AM (EST)[/font][p][font size="1" color="#FF0000"]LAST EDITED ON 12-Oct-00 AT 02:01 AM (EST)[/font]
I have a 1984 F-150 that had consistent problems with the 1 bbl. carb bolts loosening up over a period of time. After tightening the 2 bolts holding the carburetor to the manifold, they would slowly loosen up over a period of several months. This caused a rough idle and sluggishness while cold and got a little better when warmed up. Also, I had to rev it up a little to keep it idling until it had warmed up a little. I finally fixed the problem by making sure the studs were tightly screwed into the manifold, and using red loctite on the nuts. This has worked good for several years now. At first I was concerned about using the red loctite, but the nuts come off fine with only a little extra effort.
One last thing: I tried spraying carb cleaner to intially find the problem but the idle didn't change either. It was only by accident that I wiggled the carb and found that it was very loose.
Mark H.
I have a 1984 F-150 that had consistent problems with the 1 bbl. carb bolts loosening up over a period of time. After tightening the 2 bolts holding the carburetor to the manifold, they would slowly loosen up over a period of several months. This caused a rough idle and sluggishness while cold and got a little better when warmed up. Also, I had to rev it up a little to keep it idling until it had warmed up a little. I finally fixed the problem by making sure the studs were tightly screwed into the manifold, and using red loctite on the nuts. This has worked good for several years now. At first I was concerned about using the red loctite, but the nuts come off fine with only a little extra effort.
One last thing: I tried spraying carb cleaner to intially find the problem but the idle didn't change either. It was only by accident that I wiggled the carb and found that it was very loose.
Mark H.
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Posts: 359
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From: Northern Virginia
erratic/rough idle
I had a bad vacuum leak in my EGR valve - like real bad. With engine off I placed a plastic bag from a newspaper over the EGR valve and wrapped a rubber band around the base. Started the engine and the bag immediately shrank tightly around the EGR body. Replaced the EGR valve - leak gone.
Actually I think I heard the leak with one end of a quarter-inch vacuum hose in one ear and the other end near the stem (inside the body) of the valve. But not being familiar with the sound I missed it. The plastic bag was proof. (I guess I see better than I hear) What?
I had a friend that had a small vacuum leak where the throttle shaft goes through the carb body. Don't know if this area can produce a leak that is serious enough to cause your problem.
Good luck.
Raul
Actually I think I heard the leak with one end of a quarter-inch vacuum hose in one ear and the other end near the stem (inside the body) of the valve. But not being familiar with the sound I missed it. The plastic bag was proof. (I guess I see better than I hear) What?
I had a friend that had a small vacuum leak where the throttle shaft goes through the carb body. Don't know if this area can produce a leak that is serious enough to cause your problem.
Good luck.
Raul
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