alright let me just start by saying you guys are awesome and i have completely brought my truck back to life because of you guys. there are just a few little things here and there that need to be fixed and touched up. it's a 1990 3.0 TWO DOOR 4runner. and i was looking around replacing tubes and what not and i noticed the wire to this sensor behind the intake is riped out, and i've been driving with out it. but i don't know what it is.

 

Is that the engine temp sensor...(checkin' the FSM)

 

Not familiar with the 3vz, but i agree. Looks like a temp sensor.

Assuming your temp guage doesnt work?

 

They are from left to right in your picture:

1. Water Temp. Switch (3VZ–E) (sends to ECM)
2. Cold Start Injector Time Switch (switches cold start injector on for cold starts)
3. EFI Water Temp. Sensor (monitors coolant temperature for ECM)
4. Water Temp. Sender (sends to the gauge on dash)

So why have two devices sending to the ECM you might ask? One is a switch and the other is a sensor. The switch only sends an on/off kind of signal where the sensor sends a specific reading based on resistance.

Straigh from 1990 FSM:

1) WATER TEMP. SIGNAL SYSTEM
THE WATER TEMP. SENSOR DETECTS THE ENGINE COOLANT TEMP. AND HAS A BUILT–IN THERMISTOR WITH A RESISTANCE
WHICH VARIES ACCORDING TO THE WATER TEMP. THUS THE WATER TEMP. IS INPUT IN THE FORM OF A CONTROL SIGNAL
TO

TERMINAL THW OF THE TCCS ECU.
2)
THE WATER TEMP. SW TURNS ON ABOVE A SPECIFIED TEMPERATURE (105° C, 221° F). THE SIGNAL AT THIS TIME IS INPUT AS

A CONTROL SIGNAL TO TERMINAL TSW OF THE TCCS ECU.

 

ok that would make since my temp gauge in my dash still works. my temp stays right in the middle but it worries me that this one switch hasn't been sending a on/off signal for the last couple of weeks. i'm going to try to find a new connection at the junk yard tomo to solder in. would this could have caused any unseen damage due to overheating?

 

Nah. It's more of a "it's warmed up" signal to the ECU.

 

alright wow that's a load of my mind. thanks

 

All it will do is send an improper sugnal to the ECM that the truck is either at operating temp when it isn't or vice versa. The worst I could see coming from it is high emissions and a loss in fuel economy. With that said, I would fix it anyway.

 

Fluctuating idle, erratic idle, high speed miss, low speed miss, poor economy, running rich.
Yep.
Basically, if that is disconnected, your ecu thinks its -40 outside.

 

alright well that might explain poor mpg and the truck jerking (as if you tapped the brakes hard) going down the highway. just picked up new connector from junk yard so i'm going to put it in right now.

 

Would either one of these cause it to have bad cold driveability? Starts up and idles perfect when cold, but when you start to drive, it stumbles pretty bad in between shifts, shifting from one gear to another and right when you get back on it after a gear change, it stumbles and hesitates, then picks up after a second.

It's been a brutal winter here, so I've just been dealing with it, too cold to go out and ohm out sensors, not to mention 20 year old plastic connectors being brital in freezing weather. But I was figuring a temp sensor went bad, since as soon as it gets even a little bit of heat in it, it starts running fine.

 

Yes, but there are also a number of other possibilities as well. I had a similar problem back a couple of years with my 3VZE and it turned out to be the VAF (vane air flow) sensor. It'll be warm soon and you can get out there with the multimeter.