I have a 1994 Concours Deville, so far the codes i've got from the onboard comp. are S021 S044 S055. Everytime I start to take off i hear a thrrrrrrr u can feel it in the break pedal and gas pedal. Only during 0-5 mph, the car then jerks when I'm stopped pressing the brake, like for instance at a stop sign. It jerks almost as if it wants to take off. Any ideas?

abs testing itself

What you are hearing and feeling sounds like the ABS activating. It does test itself in the first 5 MPH I believe, but it does so without activation. Something is amiss, though I am not sure what. I would check the wheel speed sensors (though they should throw a code if they go bad), but it would not hurt to pull and clean the connections.

thats what i heard the "thrrrrrrrrrrrr" was, but the car acting up when im stopped not too sure about, where is the speed sensor? i'll google it but a lil help if you can. Thanks for the advice.

Wheel speed sensors are integral to the hub & bearing assembly. They plug in behind the hub.