A about 2 or 3 times a month when I start the car the rpms jump up and down from 400-700. If I tap the gas pedal or put it in drive it stop and goes back to normal. It only does it on start up every once in awhile. This is on a 98 ls400. Anyone have a clue as to what it could be?

 

Checked your codes at all?

 

Its not throwing any.

 

Pls check youre Throttle Positioning Sensor.As if there is loose connection.

 

check vacuum lines around the intake for leaks, sounds like a bit of unmetered air.

 

It could also be the IACV starting to go bad or really dirty and needs to be cleaned. I'm not saying that is the problem but here's some reading material; http://www.planetsoarer.com/IAC/iac.htm

 

Do you have this problem when AC is on?

 

Clean the throttle body. Has no IACV and a vacuum leak would be constant. Relearn the idle afterwards. Does the car have a weak battery? If so, the voltage may be dropping low enough for the ECU to forget the idle position. Cleaning the TB will allow air past the plate even if this occurs.

 

My mistake. I think I read the title as a 93. Sorry.