RPM spikes when decelerating and shifting into park or neutral

GQMGR333

MEMBER
2000 SATURN SC1
156,000 MILES

Whenever I decelerate or shift into neutral or park my RPMS SPIKE 500-1000. Different mechanics have told me different things. I have automatic 4cylander sc1. The dealer said it needed a new intake manifold gasket, so I had that done. Didn't work. The next mechanic told me it needed a tune up, new plugs and wires, valve cover gasket, crank position sensor, and idle control valve. Did all if that--still didn't work. When I pressed him as to why, he just said that it is normalnd all cars RPMS spike when you shift due to the engine loading when you shift through the transmission. Here I am $1000 laer and no better. Please help!

4 Replies

RASMATAZ

MECHANIC
75,992 POSTS

Have the throttle position sensor checked and tested, to include the following CTS and VSS sensor the computer uses their signals to control the transmission operations-could also be a vacuum switching solenoid for the transmission

Scan the computer PCM/TCM for code/s

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Wednesday, November 30th, 2011 AT 1:46 AM

SATURNTECH9

MECHANIC
30,869 POSTS

Just add to this one the transmission has no vacuum to it completely computer controled.I doubt its the tps I have replaced very few on those engines. So when you say it spikes 500-1000 rpms when you put it in park does it stay that high?Or go up that high and slowly come down?I would say possibly a bad coolant temp sensor being bad thats really common on those cars. Do you have a multimeter to do some testing?

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Wednesday, November 30th, 2011 AT 6:53 AM

GQMGR333

MEMBER
2 POSTS

Thank you for the ideas. The RPM spikes and then does slowly go down. I do not have a mulitmeter

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Wednesday, November 30th, 2011 AT 9:48 AM

SATURNTECH9

MECHANIC
30,869 POSTS

Right below where your upper radiator hose goes on there is your coolant temp sensor screwed into your head there only like 11 that is most likely bad. Also unplug it and see if the terminals are blue or green if they are then you will have to replace the connector also.

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Wednesday, November 30th, 2011 AT 6:42 PM