I have a 1992 3VZE 4x4, and it seems the idle has a mind of its own. When I start my truck up in the morning when it's cold, idle can be as high as 2,000 rpm, or, normally, ~1,600rpm. Sometimes it will "only be 900-1100rpm"... it just seems like it depends on what mood my truck is in. As he warms up, the idle speed will drop. Some days it'll drop to a normal ~800rpm, but other days it will be low enough for the idle to lope (~350) and the oil pressure will look dangerously low on the stock gauge, such that I'll blip the throttle at a stoplight to keep decent oil pressure.

Are these wild idle fluctuations normal, or is something broken? BTW, I did replace coolant temp sensor #2 that's on the back of the motor, passenger side near the firewall a few years ago. I also have a K&N air intake system w/ the less restrictive air intake tube and huge K&N cone filter. Truck has 177 / 500+k on the clock. About two years ago I had to take it to my friend's shop as it wouldn't run for snot and was stalling a lot and yet wouldn't throw a code on the dash flashing light when you jump the 2 connections under the hood w/ a paper clip. Turns out the ignition control unit that I had replaced 6 months previously with a $50 junkyard part bit the dust, so after Tim's mechanics mistakenly replaced my EGR valve and wasted a lot of my money, they figured out it was the ICU and replaced it w/ a new OEM one. That's all the major repair/mods the engine has seen in the 9 years I've owned the truck.

Thanks,
Dave

 

Ive been having the same exact problem. someone please tune in?

 

Low coolent or bad dashpot.

 

With idle problems on these motors, the first place to start is to verify the TPS resistance measurements.

 

what is a dashpot?

 

The dashpot is the little diaphragm thing on the throttle body that the throttle cam contacts when it's closing / closed. It's purpose is to keep the throttle from slamming shut. It holds the throttle open for a second or so then lets it close. This helps keep the engine from backfiring, etc. due to the rich condition that would occur if the throttle slammed closed too quickly.

 

One of the first.
Considering it's an intermittent unstable idle at cold start and warm start, it'd be the first place to look in this case. Next would be cleaning out the throttle body then checking the auxilary air valve- if it's sticking, that will mess with the idle too, so maybe a good flush of the cooling system, including flushing the coolant hoses to / from the AAV wouldn't hurt.

 

mine was doing close to the same thing as far as the idle. turns out i had a bad waterpump. check your cooling systems.