unstable RPM

My buddies 95 teg' (LS) is running as "sound" as it should be. we have come to the conclusion that it may be the intake, a ram intake, i dont know the brand. but, the engines rpm raises and falls too much for being in nuetral. then again he only paid 750 for the car and the engine is shot to hell any way, i would just like to get a 2nd, 3rd, etc. opinion on it. and possibly a solutin, with in reason of course, he was supposed to get a new gsr engine but due to funding that is out of the question.