My 01 Rx300 has a problem.. When the car turns on (8/10 times) the engine has somewhere a problem.. When you turn the key you hear the starter turn and a sec. later the car turns on, but the Tach needle only moves to 500-750RPM, and it feels like its going to stall out. Then I rev it to 2500RPM's and when it idles it goes to the normal 1000RPM idle. On other occasions the car has a very hard time to start. You turn the key and you hear the starter trying to turn the engine over, but when it finally does, the car just dies... Sometimes it takes about 8 tries to finally get it to turn over.. Whats wrong with it?
Oh I replaced the battery 2 months ago, and it was not the issue

It could be you need a new battery...Clean the battery terminals..you can also take the battery into a local auto parts store and have the battery tested its free in every auto store i have been to. My wifes minivan just had the same problem turns out she had some corosion on the battery terminals and it was causing the battery to die and not properly recharge.