Saturday, June 11, 2011

1994 olds cutlass supreme idle at 2000 rpm

The most common possibility for this high idle problem are faulty or dirty IAC motor or vacuum leak at throttle body, but if this checked ok then:---
The upper intake manifold gasket and/or a PCV vacuum lines/hoses can develop vacuum leaks with age. This type of leak can result in a higher that normal or rough idle.This could be a problem with the TPS or the PCM even.

The PCM will idle the engine at a normal speed when the TPS voltage returns to the learned base idle value. This is also called 0% throttle angle. If this throttle angle is 1% or more at idle, the PCM will assume the engine is actually off idle and raise the engine speed to prevent a decel stall. Note that another sensor using the same 5 volt reference as the TPS can momentarily glitch the reference voltage low. This will cause the TPS to send a lower base idle voltage to the PCM, which the PCM quickly records as the new learned base idle voltage. When the reference voltage returns to 5 volts, the base TPS signal voltage increases to it's previous value. The PCM now interprets this as being off idle. This will cause the throttle angle to increase to 1% (or more) and idle the engine at a fast speed.

autozone can"t run a diagnostic too old cars before 1995 models.For cars after 1995 they run scan test for free,.But as your car model is 194 , you will have to get it scanned from the autostore, who deals with OBDI tool.OBD1 tool can be available at few local auto parts store.You will just have to check out few auto repair store, they will guide to who has OBD1 scan tool.Just get the PCM scanned.This will point towards the exact fault.
Your car is equipped with a computer controlled engine management system. Try to visit any independent auto service and could scan your computer for fault or error codes. The information should pinpoint the malfunctioning components.
You need to get the thermistor checked, this is what controls the cold idle up, when it is cold the computers is told to turn the idle up and give the engine more gas. If this sensor is faulty you can and will have cold start problems,its ok when its hot but when its will play up.


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