Rough idle
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Rough idle
85 F150 4.9L carbureted
When coming to a stop out of gear the truck seems to almost die at idle speed it stays up but just sounds and feels like its dead and every once in awhile if i clutch out and slow down it will die could it possibly be Idle Air Control valve?
When coming to a stop out of gear the truck seems to almost die at idle speed it stays up but just sounds and feels like its dead and every once in awhile if i clutch out and slow down it will die could it possibly be Idle Air Control valve?
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From: Virginia
You do not have a idle air control valve on your truck. You may have a dashpot solenoid. Have you done a tune up lately? How does it run at idle otherwise? Smooth? If it doesn't run good sitting in the driveway, it probably will want to stall.
What you can also do is temp block the EGR and see if that's the problem.
What you can also do is temp block the EGR and see if that's the problem.
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From: Virginia
The carb was still mainly old school, except they did add a solenoid to try and trim the fuel a little bit at cruising speeds. And it has a throttle position sensor on it to give the computer that information.
This is as far as it got before they went to fuel injection. These old sixes with this system on them are supposed to get really good fuel mileage if it's all working. That's the problem though, they are so old half the stuff doesn't work anymore and some of it's hard to get or repair.
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From what i looked at everything has told me its an IAC attatched to the carb but its pretty much a push button type of thing please tell me what it is if its not that i already bought a replacement but after some testing it seemed like its working
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Also it runs then sitting for a few seconds it drops similar to when coming to a stop it feels like its about to die in the driveway itll do it but just stay like that when messing with part when the button isnt depressed it revs up slightly really have to listen to it unfortunantly i dont have rpm indication on cluster
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Cargo Master
Joined: Aug 2007
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From: New Zealand
Typically they looked like a round vacuum canister, with a plunger that extended out to touch the throttle linkage.
Some can disabled without creating any problem, but you need to know it's function first..........some are more necessary than others.
If this doesn't seem to add up with what you have, you will need to post a photo; but you won't have an IAC valve on a carb.
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Ok that does sound like what it is i ordered one from rockauto and it said it was the IAC either way. When i bought the truck it was pretty much a junk yard builder someone just threw what they had together to the degree of the wrong witing harness theres connectors all over the place with nothing to plug into the qouted me 1000$ to rewire the entire truck front to back so i think thats a good deal
Lead Driver
Joined: Jul 2009
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From: Sheffield, AL
Check the simple things first... the 4.9L engine hates vacuum leaks, so check all vacuum lines, carburetor hold down bolts [2] as well as manifold bolts, PCV valve and power brake booster for any sign of leakage.
The 1985 4.9L engine was computer controlled. If any part of the system [carburetor, distributor, MAP sensor, O2 sensor, temperature sensor, etc.] has been removed or is not functioning, the computer will lock the timing at the static setting [usually 10 degrees BTDC] and will make the carburetor go as rich as possible. The result will be a sluggish running engine with very poor gas mileage. Ask me how I know?
The first 2 tanks of gas in my truck returned 11 and 9 mpg. Uggg! But, things can be made better! 
The 1985 4.9L engine was computer controlled. If any part of the system [carburetor, distributor, MAP sensor, O2 sensor, temperature sensor, etc.] has been removed or is not functioning, the computer will lock the timing at the static setting [usually 10 degrees BTDC] and will make the carburetor go as rich as possible. The result will be a sluggish running engine with very poor gas mileage. Ask me how I know?
The first 2 tanks of gas in my truck returned 11 and 9 mpg. Uggg! But, things can be made better!
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