speed sensor?
 

hey guys my 97 12v has been intermittently bouncing around on the tach for like a year now.Its gotten real bad in the last few days however.The tc will lock and unlock ,the tach will bounce around and read zero then the gen and check engine light will come on .The truck will not die however.Its just a pain to drive on the highway coming out of overdrive all the time.Oh and it should be mentioned that the truck does this while in park as well.The brake lights are not being tripped either and the truck doesnt have abs as far as I know because the relay is gone in the underhood fuse box and Ive never seen any sensor lines.Anyways i cleaned the speed sensor and checked the clearance,which was way of.I set it to 50 thou.But to no avail it still is no good.ANY IDEAS??Am I missing something or do i need a new sensor,also I cant see where the connector comes off of it

how about the throttle position sensor? It's different than the engine speed sensor.

The TPS is on the throttle linkage near the p7100.

The TPS, WSS and ESS "talk" to each other through the PCM to determine what gear to be in.

ya I thought that too ,but it does it when the truck is in park as well.

Clean any and all grounds and connections you can find. worked for me.

Crank position sensor. Sometimes the wiring shorts, right around the fan hub. Check adjustment first, should be about a playing card thickness between it and the balancer.