Truck won't Idle! Please help!!
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Junior User
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Truck won't Idle! Please help!!
I have a 78 F250 4x4. I6 <NOBR>300</NOBR>. headers and an offy dp intake with an edelbrock on in. This ran great and then it got a bad vac leak which was my fault because i put the intake gasket on just by itself. I just fixed it and i sprayed carb cleaner all around where the intake bolts to the head and all around the carb and nothing was leaking. it didn't change the idle at all. I also put a new carb gasket on. It will <NOBR>cruise</NOBR> down the road great and accelerate great but now it just won't idle at all. I have to keep my foot on the gas when i pull up to a stop to keep in running. Any ideas??
Cargo Master
Joined: Sep 2007
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From: Wahpeton ND
You still have a vaccum leak? Have you checked your idle mixture settings? PCV valve stuck open. Incorect valve setting? The valve one just happened to me. Some times the angry squirls inside a 300 just stop runing due to exhaustion.
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Junior User
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there is no vacuum leak that i can find. all gaskets are new and i checked for leaks with carb spray. PCV valve is good. brake booster vac line is new. i reset the idle mixture screws to the 1 1/2 turns out but haven't fine tuned them yet. the truck won't even idle now so its hard to check anything with it running. i don't know what to try now? could be it something with the vac advance?
Lead Driver
Joined: Jul 2009
Posts: 6,477
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From: Sheffield, AL
Ranger GT2 might have been meaning that the power brake booster, itself, can develop an internal vacuum leak, so even if the hose is new and tightly secured, a leak can be present. Try temporarily removing the hose from the booster and blocking off the hose end, or remove the hose from the manifold and use a vacuum cap [or hose with a bolt]. If the engine starts to run better, you have found the leak.
Elder User
Joined: Feb 2004
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From: Indiana
Check your timing and see if it has changed or is varying any while running. You shouldn't have any vacuum advance while the engine is idling. Even if it isn't working properly it shouldn't effect the idle. Only drivability and taking off in the truck.
Try disconnecting one vacuum line at the carb or intake at a time too see if there is any difference. also try just pulling a vacumm line off and see if the motor smooths out. If it does then it is running too rich.
Try disconnecting one vacuum line at the carb or intake at a time too see if there is any difference. also try just pulling a vacumm line off and see if the motor smooths out. If it does then it is running too rich.
Postmaster
Joined: Dec 2006
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From: Spokane, WA
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Junior User
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i feel like i have tried everything. it is almost like it is running out of gas when it is idleing. could it be float adjustment? i tried adjusting the idle mixture screws and that didn't help. i plugged off the brake booster port today and it didn't change anything. plugging the vac advance line did nothing. adjusting the timing either way didn't help. spark plugs are ok. no vac leaks. it will run at idle with the choke out but its horrible and sputters. it will also run when the idle speed screw is turned way up but then its racing, but will eventuall die down still. this is driving me crazy!! i have a hunch it could be the float adjustment but i'm not posative. and other things to try?
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Junior User
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so are you saying tighten the bolts on the rockers? how much do you tighten them?
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From: LaGrande,Ore
dm300 I think you are on the right track with fuel supply. Perhaps with the work you have done something was loosened (crud) and flowed into carb. I have always found that when baffeled to go back to square one basics and check (step 1, step2, etc). If you don't live in Africa and hear hoof beats, its probably a horse, not a zebra. Haha OBCB
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Junior User
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does it matter what position the rocker is at? do you have to turn the engine every time?
Cargo Master
Joined: Sep 2007
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From: Wahpeton ND
Valve adjustments are done at top dead center on each cylinder one at a time.
I would do what I did first though. Rule everything else out. Before I messed with the valves I ruled out everything from vaccum leaks, fuel pressure, Faulty coil, spark plugs, wires, cap, rotor, ignition modual, carb, I mean everything.
I would do what I did first though. Rule everything else out. Before I messed with the valves I ruled out everything from vaccum leaks, fuel pressure, Faulty coil, spark plugs, wires, cap, rotor, ignition modual, carb, I mean everything.
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Junior User
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Valve adjustments are done at top dead center on each cylinder one at a time.
I would do what I did first though. Rule everything else out. Before I messed with the valves I ruled out everything from vaccum leaks, fuel pressure, Faulty coil, spark plugs, wires, cap, rotor, ignition modual, carb, I mean everything.
I would do what I did first though. Rule everything else out. Before I messed with the valves I ruled out everything from vaccum leaks, fuel pressure, Faulty coil, spark plugs, wires, cap, rotor, ignition modual, carb, I mean everything.