1998 Ford Explorer engine revving problem

1998 FORD EXPLORER
150,000 MILES • 6 CYL • 4WD • AUTOMATIC
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JPRESSON
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I am experiencing an issue where while under normal driving conditions the engine makes a high revving sound while the tachometer indicates that the RPMs are dropping. The RPMs are most certainly increasing at this time. When I push the accelerator pedal the issue will correct but then recur a short time thereafter. This issue has occured in all forward gears and in neutral. Since this issue occurs while the engine is in neutral I do not believe it to be a transmission issue. Can anyone offer any places to look?

I have tried to get a circuit diagram of the tach circuit but there is no individual tach circuit, it appears that the tach signal is generated by the Crankshaft Position Sensor.

Thanks in advance for any assistance.

Jon P.
Jun 27, 2009 at 4:53 AM
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SERVICE WRITER
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Have you checked for codes?
Jun 27, 2009 at 6:04 AM
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BMRFIXIT
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Sorry I didn’t fully get what is the issue with the truck can you elaborate

is it that the RPM goes up on it own

check idle air control valve remove and clean
check intake manifold gasket for leak


or you have noises when RPM up
check pulleys
check timing chain
Jun 27, 2009 at 6:05 AM
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JPRESSON
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when driving the RPMs will spike but the tachometer will actually drop

no MIL or DTC

tapping the accelerator pedal clears the issue temporarilly
Jun 27, 2009 at 6:17 AM