Idle drop
 

Is the idle supposed to drop when you remove the oil filler cap to check oil level? My car idles smooth at 900, but when I take the filler cap off the idle drops quite a bit.

1982sc stock

Yes, after the 77 model year the oil tank became a sealed system. Removing the cap or having a bad seal on the cap, allows false air, unmeasured air, into the throttle body. There is more air going into the engine than the air flow sensor is alloting fuel for.
Bruce

Thank you