I recently purchased a 1992 Lexus 300 for my wife. I could not believe this car was 20 years old. It's got 97,000 kms. And I purchased it from the original owner. They gave me the original bill of sale along with every receipt for work they have done to it over the years. I can tell you they have taken good care of it by telling you they have receipts for changing the tranny fluid 3 times in 97,000 kms. The one thing I've noticed is that the car will be idling fine when pulling up to a light or to park it and all of a sudden it will surge to around 1300-1400 rpm's from the normal idle of 800 rpm's It doesn't do it all the time but has done it a couple times to me and the wife said it has done it to her about 7-8 times in the month that we have owned it. If your not expecting it, it will surprise you. I almost hit the back end of a car in a parking lot, because I wasn't expecting it to do this.. Has anyone else had this occur? and what is the likely cause?, thx in advance.

 

Failing idle air control valve.

 

check radiator fluid level. I've seen idle surge in toyota vehicles with low radiator fluid level.
If it is the low radiator fluid level that causes surge, you'll need to figure out why the radiator fluid level is low.