About 6 months ago I started having trouble with my idle. It likes to rev up to 1500, then drop to about 1200 and repeat over and over again about once a second. This doesn't happen 100% of the time. Occasionally it will idle just fine and then start surging again when I clutch in and put it in gear. If I slowly apply gas it will continue surging at the higher rpm, but the amount it drops off each time gets smaller e.g. 1800-1650. This behavior stops right above 2000 rpm.



I've heard guesses at vacuum leak and O2 sensor. Are either of these likely culprits, or do I just need to adjust something?

if its a GSL-SE the TPS is probably needing adjustment. the FSM (www.foxed.ca) has a pretty easy method to do it. just make sure the car is hot.