speedodometer going crazy

[rharper]

2001gp gt daughters car her symptoms are she will be going down the highway when car will jerk then speed odometer will go up to 90 mph although she says she is only going 40 mph it did this a couple months ago and i replaced the icm,crank position sensor and put different coils had all of this stuff laying around now i dont want to start throwing parts at it again has anyone else had this experience any ideals

[Archon]

Is there a corresponding increase in engine speed too? Any other symptoms or other problems that could be related?

[rharper]

she said that the car did not want to go. so no increase in speed . i will have to drive tommrow myself

[1fatcat]

Wont go like no power or wont move?

[rharper]

wont go like no power its when she lets off of gas that the speed odometer increases most

[Archon]

Is the service engine soon light on? Any codes stored? Especially with the strange symptoms you're reporting, we are going to need a lot more detailed information of everything that is happening at the time in order to be able to help you.

[1fatcat]

Might be a shot in the dark, but my car acted very strange and very intermittently when the ground block corroded by the underside of the drivers door sill...but thats a 98.

[01bonneSC]

My car did the same thing in the winter a couple handfulls of times. It actually dropped to 0 mostly. Luckily I had my GPS to tell me how fast I was going. Hasnt done it since early spring. No codes or anything.

[rharper]

well i drove the car today and it drove normally i probably went 20 miles with no problems still haven't had codes read but someone told me that because the speed odometer is electronic that tells the transmission when to shift that maybe the plug going into trans needs cleaned does this sound right

[01bonneSC]

I was thinking my speed sensor might be going out.
AIRTEX Part # 5S4633
$20 from RockAuto, guess its on the back of the trans

[rharper]

thanks 01 bonne sc for your suggestions. its been hot outside but yesterday i finally got around to looking at it again. i pulled both rear wss plugs and cleaned with contact cleaner and slightly tweaked the plug contacts then put dielectric grease in the plugs then plugged them in. then moved to the front started on the left side(driver side) when i went to unplug the sensor the wires going to the wheel hub parted, hey whats this they were to short to solder back on but i had a old hub from my gmc truck that had the same end on it. after soldering a new end and cleaning, the abs and low traction light went out ,also this cured the speed odometer problem