idlesurge
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idlesurge [2010/04/09 13:09] twdorris |
idlesurge [2011/08/18 09:14] twdorris |
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| **Engine speed is primarily determined by the amount of air that is allowed to enter the cylinders.** | **Engine speed is primarily determined by the amount of air that is allowed to enter the cylinders.** | ||
| - | Normally air enters the cylinders only through the four paths through the throttle body, ISC, FIAV, BISS and throttle plate, but there are also various ways that air can leak in. Resolving idle surge means identifying and correcting the cause of too much air being admitted into the intake manifold. | + | Normally air enters the cylinders only through the four paths through the throttle body (ISC, FIAV, BISS and throttle plate), but there are also various ways that air can leak in. Resolving idle surge means identifying and correcting the cause of too much air being admitted into the intake manifold. |
| ===== Air Leaks ===== | ===== Air Leaks ===== | ||
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| * intake manifold gasket | * intake manifold gasket | ||
| * throttle body gasket | * throttle body gasket | ||
| + | * throttle body butterfly valve seals | ||
| * a damaged diaphragm in the BOV | * a damaged diaphragm in the BOV | ||
| * a damaged diaphragm in the wastegate actuator | * a damaged diaphragm in the wastegate actuator | ||
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| With all other possibilities eliminated, the remaining item to check is the throttle plate. A too-tight throttle cable can pull the thottle open, more so as the throttle-cable housing heats up, so make sure that the throttle cable has sufficient slack to allow the throttle to close to the stop even when the engine is hot. Check that the throttle is against the stop by manually rotating the throttle shaft closed. Make sure that nothing is binding the throttle shaft such as bad bearings or a badly adjusted throttle-position sensor. | With all other possibilities eliminated, the remaining item to check is the throttle plate. A too-tight throttle cable can pull the thottle open, more so as the throttle-cable housing heats up, so make sure that the throttle cable has sufficient slack to allow the throttle to close to the stop even when the engine is hot. Check that the throttle is against the stop by manually rotating the throttle shaft closed. Make sure that nothing is binding the throttle shaft such as bad bearings or a badly adjusted throttle-position sensor. | ||
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| If you are running a configured idle speed that's higher than stock, it's possible to observe a slight oscillation in idle speed even when everything else is working properly. This is because, by default, the timing tables in the ECU significantly advance ignition timing as the engine speed rises above 750 rpm, and engine speed tends to increase as ignition timing is advanced. You'll want to reduce this positive feedback by retarding the ignition timing at idle and slightly above idle. It also helps by giving the ECU's fine idle control mechanism more authority. | If you are running a configured idle speed that's higher than stock, it's possible to observe a slight oscillation in idle speed even when everything else is working properly. This is because, by default, the timing tables in the ECU significantly advance ignition timing as the engine speed rises above 750 rpm, and engine speed tends to increase as ignition timing is advanced. You'll want to reduce this positive feedback by retarding the ignition timing at idle and slightly above idle. It also helps by giving the ECU's fine idle control mechanism more authority. | ||
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| + | Also, as your idle speed setting is increased, the intended idle speed begins to get pretty close to the rpm at which the ECU cuts fuel when the idle switch is active. A good rule of thumb is to set the Coasting FC Offset to your rpm setting minus 900. For example, if your intended idle speed is 1100 rpm, set the Coasting FC Offset to 200 to raise the fuel-cut threshold by 200 rpm. Doing so also helps ensure that the idle switch will deactivate before the engine speed increases to the coasting fuel-cut threshold during no-load throttle application. | ||
idlesurge.txt ยท Last modified: 2024/03/15 11:16 (external edit)
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