The 301 redirect is working sometime and somes time not What could be the problem in below code its over a week now

Code:
RewriteCond %{HTTP_HOST} ^usedcarindelhi\.com$ [OR]

RewriteCond %{HTTP_HOST} ^www\.usedcarindelhi\.com$

RewriteRule ^/?$ "http\:\/\/www\.mycarhelpline\.com\/index\
.php\?option\=com_usedcar\&view\=category\&Itemid\=3\&location\=delhi" [R=301,L]
i basically need to move usedcarindelhi.com & www.usedcarindelhi.com to

http://www.mycarhelpline.com/index.p...location=delhi

Sometimes the 301 redirect is working making me go to mycarhelpline n sometimes am find myself on usedcarindelhi

can someone help in this pls Thanks