jgabem

What should the idle speed be (in rpm) at startup on my 1996 LS400. My cars rmp's are at 1200-1500 at startup and then drop to about 800-900 after driving it for a little while, seems like the engine sounds loud.

3UZFTE

The RPMs are normal, it's called a cold start. The engine goes into open loop and runs strictly off of memory. At this point, the vehicle usually is running rich in order to heat the engine safely. Once it becomes warm, it reduces the speed at which the engine needs to run and that usually tends to be around operating temperature. Once it hits op temp, it goes into closed loop where it runs according to the ECU fuel strategy which uses O2 sensors to relay the signal. Check your oil and gaskets, usually maintenance items will solve your issues.

PureDrifter

iTrader: (10)

still high, shouldnt be >750 at all.

iirc OEM spec is 650 +/- 100rpm