My 1990 Ls400 Lunges And Nearly Stalls At Lights But Only After Drivin

[Dean50000]

We were given a 1990 ls400 by my wife's uncle a few years ago. It sat for 3 years, decided to get it back on the road, but it is having some problems. The most dangerous one is the wild fluctuations in idle speed and power at low speeds/rpms. When I first start the car the rpms are at about 750-800 in park and 450-550 in drive. after warming up those speeds drop A LOT. 250-300 in drive and very nearly the same in park. after driving for about 9-10 mile things get really scary, rpms drop to 100 and then just as it is about to stall the rpms jump up to about 1000 and the car lunges forward then the rmps drop again and the whole cycle repeats(God help me if I'm on the highway). It continues like that for about nervewracking 4 miles then the rpms slowly climb as does the power. If I stop the car the whole lunging and nearly stalling thing begins again. I have had it checked out at a transmition shop they said the trammy was a bit low on fluid but it behaved fine on their test drive (obviously not a 9-10 mile drive). Please advise. I am planning to remove and clean the throttle body this weekend. I would really appreciate any insight you all might have for me!

[Dean50000]

Cleaned the throttle body It was not very dirty but cleaned it any way.

[Dean50000]

no change

[steve2006]

Check the IACV this is mounted at the very front of the engine with rubber hoses connected to it, this device controls the idle speed and either needs a good clean,repair or replacement.

A simple search of the forum would have revealed this.

http://us.lexusownersclub.com/forums/index.php?showtopic=30723