hey there...i have a 1993 toyota pick-up, with a newly rebuilt 22re, with a upgraded cam. before it was rebuilt it would idle high, and bounce between 1700 and 2000 RPM, we blamed it on the knock sensor since it was knocking so bad (it had a bent rod). so it sat for four months till i could get it rebuilt. after it was rebuilt the problem seemed fixed, until about a month latter. it started small, every once and a while it would rev while idling. but as time went by it got worse... now it's exactly like it was before, if not worse. i thought it was the o2 sensor so i replaced that, and while it turned off my check engine light, it didn't fix the reving . but now every once and a while the check engine light comes back on, but not for very long. i've about had it with the truck, as it broke the joint between the rear axle and the drive shaft not long ago and i had to put it in four wheel drive to get home! 
Pull the codes and see why the Check Engine light is coming on... in most cases that will point you in the right direction
