Photoshop background help please.

Im trying to blur the background on a car photo I have. I created a background layer, then used motion blur which gave me the right effect. The problem is, when I do that, the car itself, which is layer 2, ghosts the edges. Is there something Im not doing correctly? Thank you!

hard to say w/out seeing the pic, but
(a) is the background continuous, ie there's stuff under the car image?
(b) is the car itself cleanly cut out, ie doesn't have a fringe or slightly transparent border? (this can happen is you erase around the car using a brush eraser rather than a pencil eraser, eg).

Thank you for your response. The background is not continuous, meaning its the background that was taken with the photo of the car. I didnt use any type of eraser to 'cut' out the car. I used the quick selection tool/magic wand to select the car, and zoomed way in to make sure I was getting every pixel of the car, then saving it as a layer. Can I simply 'erase' the car (or background), get the motion blur I want, then put the car back? I dont know how to attach an image on this forum for you to look at. Thank you .

the problem w/ that is that when you run the blur option on the background you'll have a hole where the car used to be, and this will be what's causing your ghosty effect. you could try and fill in that hole by going around it using the clone stamp and duplicating the nearby background so that the hole under your car is smaller and the car should cover up any of the ghosted blur effeccts. by duplicating/cloning the area close to the edge and you go around the hole you should be able to cut down any apparent mismatches in colour/texture etc.

Be sure you are working on a duplicate layer above your original image layer, then If you are familiar with the bezier line tool (the pen tool), trace the car with it to define a path, convert the path to a selection and create a clipping path (layer mask) of the car. Then apply the blur filter to the original layer. If it still looks a little odd around the edges, try the following modifications to your selection, contract 1 pixel then feather 1 pixel. Then apply the mask. If you are not used to using a pen tool, it can take some getting used to but I feel this method of isolating part of a layer is a little more precise than using the "magic" tools to define a selection.