car will jump from 600-to around 900 rpms and then back again simultaneously, its having an irratic idle, it will stall out when putting it into drive if i dont have my foot on the gas pedal a little bit. It runs great except for this idle issue. I do have a smashed in downstream oxy sensor but i am not getting any codes so i dont think thats the problem. I already did the intake gaskets. So are these iac valves (1997 altima) known for causing going bad or the iac ports clogging with carbon? thanks ahead of time

if it's doing this when you first start it up in the morning ( for example ), i think you can rule out the oxygen sensor. oxygen sensors don't start to kick into action until the vehicle is warmed up. so perhaps it could be ur IAC. i would also try advancing are retarding the timing on your distributor and see if that makes any difference. if it's not where it should be, it will cause the motor to run rough at idle. so check that out and see what happens.