all of a sudden it dont idle well
Senior User
Joined: Aug 2000
Posts: 203
Likes: 0
all of a sudden it dont idle well
my 84 351W idle was set up to run smooth, now all of a sudden it idles real slow and shakes the whole truck in park, neutral and drive. but it runs like b4 when you give it gas. all the plugs are white with no traces of gas on the them. what went wrong?
Laughing Gas
Joined: Jul 2001
Posts: 1,019
Likes: 3
From: Bismarck, ND
all of a sudden it dont idle well
Sounds as if you've developed a vacuum leak somewhere. Possibly one of the hard plastic vacuum capillaries (tubes)? They're famous for getting hard and brittle and cracking with age.....
Laughing Gas
Joined: Jul 2001
Posts: 1,019
Likes: 3
From: Bismarck, ND
all of a sudden it dont idle well
It's always possible. I'd also check around the EGR valve and carburetor. You can get a can of carb cleaner or WD40 with the little straw and spot spray around suspect areas like the intake manifold and carb base with the engine idling. If the idle changes at a point (due to the engine sucking in the spray), you've found a leak. Also, though not related to the bumpy roads, the EGR valves have a habit of becoming carboned up. It may be worth picking up a new gasket and taking yours off to check the intake port and valve and cleaning, if necessary. Good luck! 
Laughing Gas
Joined: Jul 2001
Posts: 1,019
Likes: 3
From: Bismarck, ND
all of a sudden it dont idle well
Could be a number of things, including basic tune-up items, like plugs, cap, rotor, timing, etc., or even carb / choke adjustment. Assuming all these are good, and sticking to the vacuum leak theory, do you notice any difference (more frequency of poor running) when you step on the brake, like to shift into reverse or stop after backing up? Many times when the power brake boosters will start to go bad, they'll develop an internal vacuum leak that will show up when you step on the pedal. Just another thought.....
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Senior User
Joined: Aug 2000
Posts: 203
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all of a sudden it dont idle well
the plugs are new, the cap, rotor and wires look new, the carb was rebuilt by me with a kit from the local store. also when i drive the brake pedal seal in the firewall has a hissing noise, that blows a little air. how much is a brake booster?
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Laughing Gas
Joined: Jul 2001
Posts: 1,019
Likes: 3
From: Bismarck, ND
all of a sudden it dont idle well
I just bought a booster and master cylinder a couple of months ago. I don't recall the exact price, but I believe it was between $85 and $110 for both. If you've got any miles on your m/c at all, buy the two as an assembly. As I recall, the booster without the m/c was almost the same price as the one with it.
