You can check buy removing it? You can look for any gunk that may have been built up ...if it needs a cleaning you can use that electrical spraying shit. If you read other nissan forums the 240sx is notorious for having idle problems. What ended up being my problem was the spark plugs i put in...i had bosch +4platnium which would make my car idle like shit, took those out and put in NGK iridiums, problem solved. I take it your not getting any codes? Usually a O2 sensor or Maf would come up.