What is the high pitch noise the 6 cylinder engine makes when running on a 1994 land cruiser and why does it take so long for the high RPM after startup to slow down?

Answer 1

When you start the motor, and it's cold the fan clutch will make something like the noise you describe, until the rpms reach a point at which it disengages and freewheels along (it only works below 2200 rpm or so). How long the motor will remain at fast idle is something that the coolant temperature sensor will determine, so you could have a problem there and the symptom be an unusually long time at 1500-1800 rpm fast idle. Ben There is a common condition where the 1FZFE motor will idle too high during warm up. The fast idle speed seems to vary from vehicle to vehicle, and is usually somewhere between 1,200 and 2,000 rev/min. It is controlled by the ISC (idle speed control) valve. This valve is simply a device which allows more or less air (as determined by ECU) to bypass the throttle butterfly, and thus affect idle speed. In other words; without the throttle butterfly being opened by the driver, the ECU will allow more air to bypass for an increase in idle speed, or less air to bypass for a reduction in idle speed. On cold start, sensors seeing low temperature cause the ECU to open the ISC valve fully. "Excessive" cold start idle speed can be reduced by "fiddling" with the ISC valve to shorten it's stroke. For a full write-up of the modification, including high resolution photographs, go to http://tinyurl.com/2jcrlk. Dave