keep getting reduced engine speed

Would need a little more information to properly diag. this problem. What do you mean by reduced engine speed? Does the engine lose power? Is the transmission slipping? Does it run rough when engine speed reduces? Does it reduce smoothly or is it a rough reduction? Does it matter if engine is hot or cold? Answer these so we can help you better. thanks

last time happen did run rough, before that no. has happened both when engine has been cold and hot and yes loses power usually it is smoothly

It reduces smoothly when stopped it ildles rought . I turn the engine off for a few minutes then it will run ok for a while be it happens again