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Old 11-06-2005, 07:43 PM   #1
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The high idle...

well, after working with my 89' four cylinder for about 2 months, chasing down all the vacuum lines, replacing the pcv valve and the valve cover gasket, I can't figure out why it's idling high. It'll go to like 2000 rpm in neutral... I know it's been discussed before, so, anyone have any info?
Actually, has anyone successfully fixed this? lol

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Old 11-06-2005, 09:10 PM   #2
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Is it Fuel injection or Carb?

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Old 11-06-2005, 10:13 PM   #3
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Fuel Injection...... It's the same mess everyone seems to be having with these.
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Old 11-06-2005, 10:36 PM   #4
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Perhaps the Throttle position sensor?
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Old 11-07-2005, 07:24 AM   #5
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Is it staying at 2000rpm or just going up to that then idling down? If it's staying at that, check the throttle body to manifold seal. If it's leaking around the throttle body it could cause that. Also check your FSM for the water temp sensor test. If it thinks it's constantly cold, it might idle up. Fuel injection can be a pain, but the systems in these jeeps are very simple. Total sensors (if I miss something let me know) being used in the EFI: water temp, intake air temp, manifold absolute pressure, oxygen, throttle position and oil pressure (basic kill switch setup if the pressure drops). Some older systems had a component that would stop the throttle plate from dropping completely closed too fast. It was usually nothing more than a buffer that the throttle lever would hit and it would slowly drop back from that point to idle. Sometimes those would get stuck, but I haven't seen that on a jeep system. Get a can of dielectric grease and as you test your sensors fill the connectors with the grease and push them together several times to clean the contacts and ensure a good connection. The grease will stop corosion, keep water out and maintain a tighter contact. I swear by it for everything electrical, especially in an offroad vehicle (I tend to drown mine in water quite often).
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Old 11-07-2005, 08:48 AM   #6
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Solid 2000. never does it drop.... if I plug up the PCV it drops to normal 700ish.
I'm going to udjust the hidden(aparently) idle screw, but I don't have a diagram for the underside of the TB.(thanks Haynes.)
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Old 11-07-2005, 09:21 AM   #7
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Hmmmm, serious vacuum issue somewhere. You have a leak around your intake manifold. Might not sound desirable, but it's cheap and would save you alot of trouble later if you pull your intake manifold and replace the gaskets in EVERYTHING attached. Gaskets are cheaper than sensors so if nothing else it's probably a needed job anyhow.
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Old 11-07-2005, 09:45 AM   #8
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In the meantime, since this is my daily driver, can someone point me to the adjustment screw? and thanks for the help!
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Old 11-07-2005, 10:31 AM   #9
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If you have a leak at your manifold, I'll bet you can back that screw off the stop and it won't lower the idle. But, sorry, I'm not sure where the adjustment screw would be at exactly, but the typical position is near the throttle lever.
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Old 11-07-2005, 12:26 PM   #10
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So, I go out to work on it today, and, the first thing I try is the MAP sensor, pull the vac line off the thing and the idle goes down. So, although this is not a fix by any means, what would happen if I just left it off?
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Old 11-07-2005, 02:57 PM   #11
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Depends. You could start to run too lean or too rich depending on how the ECU compensates for the flat reading.
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Old 11-13-2005, 08:24 PM   #12
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Hey bro,
before you start yanking hoses, wires and your hair out, PLEASE start the beast, and let it run. Get a can of carb cleaner and spray around the manifold, and any area that pulls vacuum. If the idle changes, that is the source of your leak! This works..trust me. I have had the idle gremlin driving me crazy on my jeep and mustang in the past, and this test will help if it is a vacuum problem.
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Old 11-14-2005, 07:04 AM   #13
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Gret advice, I didn't think about that.
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Old 11-15-2005, 08:02 PM   #14
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you can also use a propane torch...not lit of course. the propane will also make the motor rev higher.
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Old 11-15-2005, 10:42 PM   #15
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That is a good tip to take note of! Oh by the way, nice jeep.

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