I am not talking about PR.I am talking about SERP.As far i know there is no link in between PR and SERP.You may find many sites, which has no PR but ranked well.
What kind of promotional tactics you are using for website. Try to concentrate on building more backlinks for getting the ranking through the targeted keywords of the website.
Searching keywords daily is not at all harmful, it won't even have any effects on your rankings. But it is harmful to you though and your time. Try using your time to promote and research how to improve things with the site.