1UZ-FE LS400

I had the exact same problem with my LS400. I changed the throttle body sensor and took off the throttle body and plenuim attatched to it and found that i had MAJOR carbon build up covering the inside of it. Take carbourator cleanor or paint thinner and clean the carbon out of both of them. I haven't had the problem since. Try this and if it doesnt work then you might have to resort to an idle air control sensor, which will run you around $500. ouch. But doing this will most likely help alot and give you back your feul economy and precious horses you know youre not getting :)

'97LS w/ 180k, timing belt and major tuneup scheduled for next week.

The LS was parked outside at the airport for 4 days, temperature was low 40's at night and around 65 during the day. The last day was rainy. The normally flawless LS started fine but revved up to 20k rpm, then dropped to about 2k. It then proceeded to bounce around in a less than smooth fashion. It continued until the car was warmed up, then it seemed to run ok, maybe a little rich. It seemed to start ok when cold and ran fine today. The check engine light did not come on. Any ideas? I would like to figure out what it was before the major tune and timing belt. Thank you in advance.