high idle
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high idle
I have a 1989 bronco xlt. It is running rough. When I start it up it idles at 2000 rpms. I put it in to drive and the rpms drop down to normal. But if I put it in neutral or park the idle jumps back up. I thought there was a vaccum leak. So I used carb cleaner. No increased rpms. I need help. My engine sounds like it's about to take off like a plane.
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Joined: Sep 2002
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From: Gateway to the West
Does it drop to normal in drive or does it idle high enough in drive to pull itself along? Do the throttle plates close completely with your foot off the accelerator? Can you bring the idle down by covering the throttle bores with your hands cupped over them? Does the idle eventually come down once the truck has warmed up completely? One last question... Does the engine start very quickly and rev high as soon as it turns over?
Sorry for answering your question with more questions but with a bit more info we may be able to help pinpoint the problem.
If you can't stall or slow the idle by starving the engine for air, you almost certainly have a vacuum leak. There is an outside chance that part of the throttle body has been screwed with but if you are the only one who has been under the hood, its not likely.
One last point... Welcome to FTE and the Big Bronco Forum. We will do our best to get you the most accurate info we can dig up.
Sorry for answering your question with more questions but with a bit more info we may be able to help pinpoint the problem.
If you can't stall or slow the idle by starving the engine for air, you almost certainly have a vacuum leak. There is an outside chance that part of the throttle body has been screwed with but if you are the only one who has been under the hood, its not likely.
One last point... Welcome to FTE and the Big Bronco Forum. We will do our best to get you the most accurate info we can dig up.
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Yes it does drop to normal in drive. I live on a hill and I dont need to press on the gas to get to the top. I need to check the plates to see if they close. The idle does not come down at all. Only when I put it in gear. Yes the engine start very quickly and rev high as soon as it turns over. All this started when I went to one of those jiffy lube places to get the oil changed. Thank you for helping...
Lead Driver
Joined: Sep 2002
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From: Gateway to the West
There is a potential that you have an injector (or a couple) leaking down while the engine is off. You can check this by taking a pressure reading at the Schrader (tire stem type) valve on the fuel rail every few minutes through about ten minutes after the engine is shut off. The fuel rail should hold 35-40 PSI fuel pressure for at least the first ten minutes after the engine is shut off. If not, I would suggest pulling the spark plugs (one at a time) and checking to see if there is enough leak down from any of the injectors to make the tips wet.
The other possibility is that the idle stop screw has been messed with. However if this just started happening the idle stop screw doesn't just move on its own. If you suspect this could have happened, you can check to see if the screw needs to be reset to factory specs. with a quick test.
The other possibility is that the idle stop screw has been messed with. However if this just started happening the idle stop screw doesn't just move on its own. If you suspect this could have happened, you can check to see if the screw needs to be reset to factory specs. with a quick test.
Lead Driver
Joined: Sep 2002
Posts: 9,182
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From: Gateway to the West
Definitely into the realm of code pulling and IAC cleaning. Something else you may want to have a look at (but don't mess with it yet) is the throttle plate stop screw. If it has been "adjusted" by someone you may have to go through the slightly tedious process of resetting it. But this should not even be attempted until you have ruled out a stuck/dirty IAC or any errant fault codes in the system. The IAC is mounted with two bolts to the driver's side of the throttle body and has about an 1.5-2" diameter barrel-shaped solenoid with a connector and pigtail coming off of it.
The stop screw is just as you might expect. It is a mechanical stop to keep the throttle plates from slamming shut and sticking in the bores of the throttle body. (There are quite a few misinformed or just ignorant folk who seem to think this screw is an idle adjustment. IT IS NOT! However, it doesn't stop some from messing with it. If it has been run IN it will actually hold the throttle plates open too far causing the truck to idle too high and taking the control of idle speed AWAY from the IAC (Idle Air Control) valve and solenoid. Idle is controlled by the IAC and the computer. There is no human interface or adjustability for it... period.
The stop screw is just as you might expect. It is a mechanical stop to keep the throttle plates from slamming shut and sticking in the bores of the throttle body. (There are quite a few misinformed or just ignorant folk who seem to think this screw is an idle adjustment. IT IS NOT! However, it doesn't stop some from messing with it. If it has been run IN it will actually hold the throttle plates open too far causing the truck to idle too high and taking the control of idle speed AWAY from the IAC (Idle Air Control) valve and solenoid. Idle is controlled by the IAC and the computer. There is no human interface or adjustability for it... period.
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Was this ever resolved? I have the exact issue
I have a 1989 bronco xlt. It is running rough. When I start it up it idles at 2000 rpms. I put it in to drive and the rpms drop down to normal. But if I put it in neutral or park the idle jumps back up. I thought there was a vaccum leak. So I used carb cleaner. No increased rpms. I need help. My engine sounds like it's about to take off like a plane.
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