CoonDog

I'm a newbie. I'm not a mechanic, but I've learned something that may help some of you. There are many very bright people here who know much more than I ever will. I ask you to give me the benefit of the doubt if I have oversimplified this, or left something out.

This may be a long post...I have an '87 4Runner with the turbo. I bought it a year and a half ago, and the mileage has been poor, 11 to 13 mpg. In reading the posts here, I learned that most people are reporting the same numbers. The transmission would not down shift when the engine was warm. I was getting a miss ever so often, but not regular. I changed the plugs, wires, etc. ... no help. I read all the posts about the TPS, MAFS, et al. I discovered the O2 Sensor was not working, and replaced it. No help. Then, I found some and answers.

There are two sensors located in front of the thermostat housing on the 22RTE. One of them is a water temp gauge, and the other is a sensor to control the radiator fan. This sensor is called an Electronic Coolant Temperature Sensor. It not only tells the computer when to start the radiator fan in relation to the coolant temperature, it also sends a message to the computer to regulate the fuel being sent to the cylinders. When cold, the sensor tells the computer to dump more fuel. As the engine warms, the sensor tells the computer to dump less. Consequently, the O2 sensor is not going to have much affect on fuel economy if the ECT sensor is malfunctional. After all, the O2 sensor works with exhaust gases, AFTER the fuel is burned. No matter what the O2 sensors says to the computer, it won't change fuel consumption if the engine is reading "cold" all the time no matter what the coolant temperature is. When the engine warms, it takes less fuel, and consequently burns less gas. The only way the computer knows if the engine is warm is if the ECT sensor tells the computer the engine is warm. These two sensors (O2 and ECT) work in tandem to control fuel economy and emissions. The TPS on my truck may need to be adjusted. I won't know until I've run through this tank.

I pulled the sensor, and discovered that it was corroded, and that the electric connector inside the plastic housing was corroded. (There is no code associated with this malfunction.) I went to Toyota, and was able to find a replacement part for 82.00. The parts man also located the same part at NAPA for 42.00. I replaced it after repairing the electric connector.

As soon as I started the truck, the idle, which had been at about 750 rpm, went to 1750 RPM! This told me the sensor was working. After the engine warmed up, the idle did not diminish to a normal speed. I reset the idle, and guess what? My transmission functions properly...shifts when it is supposed to so I don't have to use the ECT power button for normal driving. I don't know yet whether the mileage will increase, because I filled the tank just before making the repairs. Plus, I haven't noticed the occasional miss I was getting before. I'll let you know how it turns out...if you are interested.