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1998 Ford Explorer engine revving problem

Tiny
JPRESSON
  • MEMBER
  • 1998 FORD EXPLORER
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 150,000 MILES
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.
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Saturday, June 27th, 2009 AT 4:53 AM

3 Replies

Tiny
SERVICE WRITER
  • MECHANIC
  • 9,123 POSTS
Have you checked for codes?
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Saturday, June 27th, 2009 AT 6:04 AM
Tiny
BMRFIXIT
  • MECHANIC
  • 19,053 POSTS
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
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Saturday, June 27th, 2009 AT 6:05 AM
Tiny
JPRESSON
  • MEMBER
  • 2 POSTS
When driving the RPMs will spike but the tachometer will actually drop

no MIL or DTC

tapping the accelerator pedal clears the issue temporarilly
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Saturday, June 27th, 2009 AT 6:17 AM

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