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| fast idle; metro is idling faster than it should | |
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| Tweet Topic Started: Dec 25 2016, 02:10 PM (506 Views) | |
| paulsteger | Dec 25 2016, 02:10 PM Post #1 |
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Fresh Fish
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my 94 metro with 275000 suddenly started idling fast even when warmed up doesnt seem to be a vacuum leak because I checked with a guage at the power brake port and vac was steady at about 19" It is as though it is a very cold day and I just started it. But idle never comes down Runs well other wise. I reseated connectors of all sensor type plugs near the throttle body--no help. Throttle valve is not sticking or held open there is a solenoid plunger that is made to hold the throttle plate open a bit, but its not touching the mechanism, so its not a factor. How does the computer control airflow into the throttle body when the throttle plate is fully closed |
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| MR1 Kingsbury | Dec 25 2016, 02:24 PM Post #2 |
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Exp. builder/rebuilder
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there is a small filter in the vacuum line from the tb to the firewall at the manifold absolute pressure sensor recheck/replace that line and/or clean the filter. check the electrical connection on the same.
Edited by MR1 Kingsbury, Dec 25 2016, 02:25 PM.
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| Stubby79 | Dec 25 2016, 08:12 PM Post #3 |
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There are two methods for controlling the idle air flow...an IAC and tan ISC. The one opens your throttle as required, the other lets air bypass it. If you have a black box attached to the back of your throttle body, then you have the ISC motor. And if it isn't opening it, as you described, then it's something else. If you don't have the black box, then I don't know what you're talking about with a solenoid, as the IAC is seperate. ISC: ![]() IAC: ![]() Which do you have? You could still have a small vacuum leak at one of the smaller hoses without losing all vacuum. Your EGR could be stuck open or leaking/sucking in fresh air. Something else could be letting air in. Get back to us on which setup you have first though. |
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| MR1 Kingsbury | Dec 25 2016, 11:40 PM Post #4 |
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Exp. builder/rebuilder
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NIce linked pics..... It sounds like the description of an ISC. They can be a pain in the ass, but it seems in your case there is a vacuum leak or a map sensor system failure/ And don't overlook the problematic EGR system.... You gotta check all that stuff out. Warm vacuum lines may leak more than cold ones... replace or inspect. Edited by MR1 Kingsbury, Dec 25 2016, 11:42 PM.
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| Hanuman | Dec 26 2016, 09:55 PM Post #5 |
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"The Almighty Grounds Cleaner"
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*Can a moderator move this thread to the engine section?* Check all the vacuum l8nes for leaks. Some times the tbi gasket can fail causing a big vacuum leak. Check the egr valve where it bolts to the intake manifold for leaks. Check the brake booster, booster vacuum line and the rubber seal for leaks. |
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