I think I might have a leak somewhere. Car starts easily and idles smooth at around 800 rpms for about 30 sec or so. Then the rpms fluctuate some. Drop down to around 500 and back up. Car revs smooth when you get on the gas. You can hold it at higher rpms and it runs nice and smooth. Let back off and it starts fluctuating again. The mpg meter fluctuates with the rpms too. Where should I look for a problem? How should I check for a problem? I just changed all the plugs, wires, distributer cap, rotor. I was thinking that it probably is a small air leak or something? Car has chip, k&n filter (stock replacement), magnaflow muffler and cat. Could the O2 sensor need replacing? Don't know if it has ever been replaced? TIA Lots of knowledge on this board. Great help for a newbie like me

 

sounds like after the car warms up, the idle air valve closes but there's still an open leak. i'd start my check at that vacuum line area near the idle air and aux air valves.

 

get a pressure tester for the intake, and pressurize it to 10PSI..listen for hissing....

 

I found the problem. The J boot thing had a crack in it causing a small air leak. When I squeezed the boot, rpm changed. Thank goodness it was something easy and cheap!