Volvo 99.. C70 .. bogs when put in drive
 

I have a 99 2.4t convertible volvo c70 runs great except sometimes when i put in drive or low gear it wants to bog really low.. sometimes even cuts off. Any ideas? Im clueless. Its not throwing an engine light. Then another thing is sometimes when you go to stop at a sign .. it bogs to really low rpms. Thanks.