First thing First-Welcome to RC Universe! You'll find people here are usually very helpful when someone has a problem to work out.

Like Bob said, the more information you give the people here the easier it is to help. From your statement I'm guessing you have a buggy with a Nitro motor in it. The manual should tell you where to set the needle valve, just close it (but don't over tighten it) and open it the recommended amount of turns. If it shot up in RPMs when you started it you may have to reverse the servo direction, it sound like it's wide open when the throttle on the radio is at idle. At any rate tell us what brand of engine you have and the size, (like .26 etc.). If this is a glow (nitro) motor you may want to post you question in the Glow Engines forum for better help with your problem, this one is for Gasoline (petrol) engines.

Good luck.