96 sable impeller speed sensor

I have a 96 sable with 121k miles. 3.0 engine (not the 24-valve). I'm experiencing the following problems: with my foot on the brake, when I shift from park to drive or reverse, the engine rpms increase from idle to about 1200 rpms, and the transmission slams very hard into gear. It's especially bad when the car is cold (I assume because the idle speed is already higher when cold). Also, when accelerating from a stop, the shift from first to second is very hard (slams) unless I accelerate extremely gently ("granny-like", but no offence intended). Check engine light is on, and the code reads IMPELLER SPEED SENSOR SYSTEM MALFUNCTION. Does anyone know where this is located and can I change it myself. I called the local tranny shop and they told me about $125.00 to $200.00 to replace it, so I don't think it should be a huge deal, but don't know how locate/replace it. My Haynes manual doesn't address it at all. I'm a brand-new subscriber to AF but from what I've read regarding answers to others ?'s, I'm really looking to forward to seeing replies. Thanks so much for any info/advise offered.

I'm not sure what the problem is, but to be sure, have it hooked up to a diagnostic machine before you anything. Auto Zone will do it for free, if there is one near you. Good luck!

thanks for the reply. I did have AZ test it, and they informed me what the code means (IMPELLER SPEED...). unfortunately, I still haven't found anyone to forward the info on locating and replacing it. Oh well, I tried. Hope you get better responses on your requests.....

Do you know what the actual code # is? P0500, P0501, P0502, P0720?? I don't see any reference to IMPELLER in the code listings in Hayes, but the above OBDII codes deal with vehicle speed sensor/output shaft speed sensor.
The VSS (99 and earlier) or OSS (2000 and newer) in the transaxle control the shifting of the tranny and supply the computer with speed info for the speedometer, etc. This is a ~$30-40 part and may be the problem. Look in your Hayes (#36075) manual on page 6-14 (#13).

Also check the Trans Range sensor, This is the unit that the gear shift cable connects to.
It tells the computer what gear the tranny is in and affects the EGR system, idle speed and transaxle torque converter lockup. (this is text from the Hayes manual) If this is the problem, there should be error codes stored in the computer.
Good luck.