390 Weird Idle
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Cross-Country
Joined: Aug 2020
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I'm going to pick up a new gasket today which will also act as a spacer because of its thickness. If I get around to it, I'll borrow my buddys timing light and check my timing. Hopefully this solves my issue. If not, i guess ill move onto the brake booster? I know Ozzie H. said something about something possibly binding up but just because of what is happening, I swear its a vacuum leak. The other day after driving it for 5 minutes when warm, idle went down to nearly 200 and just surged and wouldn't idle higher than that. Went home and parked it, started it yesterday and let it warm up and drove it for a few and before driving it, it was idling around 500-600 which is pretty good. After driving it, it was idling at around 800-1000. It makes no sense to me and I need to fix it because I've put it off for too long.
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To check your booster you can either unhook it and plug the hose. or you can idle the engine down and shut it off. then press on the brake pedal, if your diaphragm is good you'll feel and hear it and feel a push. but if it was bad you should be able to tell because your brakes would suck. cover the air horn with a rag while it's idling and you'll know if you have a vacuum leak. unless it's intermittent.
When I say check your timing I'm not saying you're out of spec it would be more of a problem with your advance mechanisms, either mechanical or vacuum. if they're sticking it would really effect your idle. what you really need it to check it when it's not idling properly not when it is.
Also check the fast idle cam and linkage to be sure it's functioning properly.
When I say check your timing I'm not saying you're out of spec it would be more of a problem with your advance mechanisms, either mechanical or vacuum. if they're sticking it would really effect your idle. what you really need it to check it when it's not idling properly not when it is.
Also check the fast idle cam and linkage to be sure it's functioning properly.
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Cross-Country
Joined: Aug 2020
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So I put the new gasket on and replaced the bolts with studs and it was super easy. Drove around the block a few times with the idle set to 650 and after driving low and behold it goes back up to 1000. If I quickly slammed the throttle it seemed to make it go down but not every time I did it. I set the idle at 500 and it seems to like that even after 30 minutes of driving. So does that mean then that something is binding up?
I don’t even know. I hope it continues to idle at 500 and not surge or go up.
I don’t even know. I hope it continues to idle at 500 and not surge or go up.
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