bluezucsky

Steve, Thank you for the pointer. I went through the discussion thread, however, my issue is different as follows. When I start the cold engine, the car idles at 1400RPM. Before putting the transmission in drive, if I let the car warm up for 2 minutes, the RPM drop to 1100 (as an example). Now if I drive the car and even if the temp is normal when I lift my foot off the gas pedal, the engine still operating at 1100RPM (whatever was the RPM at the time I moved from Park or Neutral to Drive). Now if I bring the car to a stop, the RPM still stay at 1100 until, the trans is moved to Neutral. You have to stand in Neutral for 5 seconds and RPM will return to 650RPM. No other issues at all. No check-engine lights or anything. Any ideas. Thanks again.

I have 90 LS400 with 140k miles. When the car is started with engine temp below normal (as in mornings or car has cooled down for few hours), the idle speed stays at 1400 RPM if the car is driven without waiting for temp to get normal (in the middle). The only way to get the idle speed to normal 600 RPM (even after engine is at normal temp) is to stop the car, place it in neutral and wait for a few seconds, until idle speed returns to 600 RPM. Shifting to neutral with the moving car will not work. It has to be stopped. In summer I can usually wait long enough for car to warm up to normal temp before driving it which returns idle speed to 600RPM. However, in winter it takes a little while for engine to warm up, so, I want to get the problem fixed. Any ideas for this strange behavior? I hope this is not by design. BTW, I have new plugs, filter. Car has excellent emissions etc. Regards.