'94 SL motor revving to high in drive even higher in neutral----SENSOR?

Maybe someone can help me with this one. I think I had the same
problem 2 1/2 years ago. Then it was winter and it would happen once
the engine warmed up. Now, right at start up. At the light,the tach is
at 1.5
If I shift it into neutral it jumps up to 2 and change, hovers for 2
or 3 seconds and then slowly drops down to 1.5.
I still have the NAPA receipt from the mech and it says cooling
sensor.
Is this the problem? Is it racing due to a faulty reading from this
thing?
Where is it and how do I change it?

Thank you.

Rob

 

I'd almost GUARANTEE it!!!
There are two temperature sensors on the transmission side of the
engine, located in the head just above the engine block.
The top one connects only to the guage in the instrument panel.
The lower one is what the PCM uses to determine the mixture and
whatnot.
A bad one will result in the high idle you have described.
You will probably find that while rolling, in neutral, the rpm will be
about 2000 and will decline to 1500 when you come to a stop.
In this condition, your vehicle will fail any emissions test, your
Catalytic converter will possibly overheat and the engine will probably
run too hot as the PCM "believes" the engine is running WAY too cold.
(the sensor typically fails in a way in which the resistance is far,
far higher than it should be).
You will first need to CAREFULLY remove the electrical connection. I
used a hook-shaped dental tool to gently pry one latch side away from
the sensor and then the other. Pry it too far and you will break off
the latch.
It will be easy enough to replace the sensor with a deep socket - dont
know right off what the size is, I think its something like 10 or 12mm.

The sensor is available from Autozone for aproximately $9.
You will need to drain most of your coolant before removing the old
one, or it will leak out of the fitting point when your remove the
sensor. Loosen the coolant reservoir cap to speed up the draining
process.
At this point you may want to replace your coolant, as it may be
overdue for a changeout anyway, but please dont potentially expose any
animals to it as it will taste sweet - they will drink it and it will
kill them in a most inhumane way.
I used teflon tape around the threads to guarantee a good seal and
slick install, but the threads will probably already have some red
sealant poo painted on the threads anyway - mine did.
I've been through this process with both my 94 and 95 SC2 Saturn. Both
had the same symptoms you have described - in both cases the idle
returned to a nice, normal 750 to 800 rpm.
-Wavy

 

Wavy, thanks a million!
Just one thing:

Can you narrow down exactly where this thing is? Do I get it from
underneath or is it accessible from up top? I don't see it.

Rob

 

Definately accessable from above. Not accessable from below.

I should have mentioned that to get to it, you'll need to remove the
plastic air intake ducting from between the air cleaner box and the
aluminum end of the intake manifold.

At least that's how it is on a SC2 with the independant (4) fuel
injectors. I'm not familiar with the SL or if your car has a "throttle
body" injector, but regardless of the specific model, I'm pretty sure
that theres an air duct or air cleaner component in that area - which
would otherwise be in the way.

-WaV

 

WAVY, YOU DA MAN!!!


It no longer feels like I'm holding back a hungry doberman at the
light. Thanks for the dental pick tip for the wire cap. All I had was
a small pocket plaque scraper but it worked fine. All told it took
about 30 minutes and spent $11 for the sensor at NAPA. Last time it
cost me $80.

Thank you.
Rob

 

Nah, Rob -

YOU Da Man!
'Cause rather than give in to your mechanical insecurities and fold-in
to guys with bad teeth and dirty fingernails - you sought out an answer
and you WORKED IT OUT.

-WaVy
Defeating the laws of Entropy
One Saturn at a time.

 

Wavy,
Hi I had the sensor changed when they changed the water pump and my
mechanic had trouble with it when installing the sensor and had to make
some kind of adjustment to the sensor in my 94 SW2. When I got the car
back the light was on for over heating after I bought (and returned) a
reservoir I found the plug disconnected from the plastic reservoir and
that turned off the light. I took the car to MI from NJ and put over 2K
miles on her without a problem but the other night I was driving to NYC
in the rain and at 2 ½ hrs of driving (lots of detours) the check
engine light came on and the next morning it was off and never came on
again. I recall when driving that night the engine revved up to 3K for
no reason and the temp was ½ way on the dial so indicating OK. Is this
temp sensor related because it revved up?
Thanks Linda
94 SW2 168K on body 75K on new motor & trans