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Toyota pick up - fast idle, surging

I have a 95 Toyota t-100 pickup, 4 cylinder, 5 speed that surges or idles fast all the time. T&R suggested on this weeks show that it most likely is the coolant temp sensor. That’s great…but I can’t find it on the engine anywhere. Please help. Thanks Dale

The temp sensor is often located on or near the thermostat housing. Not always, however.

Other possibilities for a surging idle are a vacuum leak and a bad or dirty Idle Control Valve.

Thanks, but the only thing I could find near the thermostat housing is the gauge sensor which is working fine gauge reads toward the center - unplug sensor and gauge falls to nothing.

Maybe the sender you found signals the computer, too.

Well I did what I usually do and went out and bought one and then proceeded to look for the same item on the engine. It does not match. One I purchased is much larger. But maybe I was given the wrong part or the old engine swap trick beforeI bought the truck.

I should have specified - the one I purchased was much larger than the unit for the gauge.

Assuming the engine is a 22R-E (I don’t think they got to the 2/3RZ until 96), I doubt the CTS is the problem. These particular engines have a cold idle air control that gets warm by very tiny coolant hoses from the thermostat housing and the passenger side bypass pipe. They plug up easily after over ten years, and then the IAC never knows the engine is warm. Flushing rarely cleans them, since they plug solid. The fix is to drain the coolant, remove the hoses and bypass pipes and physically clean them all with a wire and rinse water (replace any hoses that look questionable). Refilling the coolant is tricky because of the downward bend in the upper radiator hose. Creating a Vesuvius is very easy, so it’s adviseable to do several warmup/cooldown cycles with the radiator cap on, removing the cap when it’s cooled off and topping up the radiator till all the air is gone.

It’s easy to determine if this is the problem: when the temp guage shows the engine is warm, if the hoses are not too hot to touch comfortably, that’s it.

As I was looking for the small hoses and not having any success I noticed yellow paint marker numbers on the side of the engine which lead me to believe the engine has come from the junk yard. So from your advice I looked for an engine number and found a sticker on top F2Rz-N73. I guess that changes things. I appreciate very much the detailed advice you gave me - any other help would be great.

Yup, I was wrong, then…it IS a 2RZ. Since I have a Tacoma with that engine, I’ll locate the CTS tomorrow when I’m back where the truck is, and let you know what I find.

It’s nowhere near the thermostat housing…it’s buried under the mass of wiring and hoses toward the rear of the air intake plenum, around cylinders 3 & 4. Looks like a real pain to get to. BTW, if the CTS is really kaput, I’d expect it to set a trouble code, lighting the “Check Engine” light. Might be worth it to get the truck hooked up to an engine analyzer and check the data stream - that’ll show, among other things, the actual temperature the CTS is sending. If the engine is warmed up and doing its idle fluctuation, but the CTS says the temp is 40 below, you know you’ve located the problem. If, on the other hand, it’s reporting a reasonable temp, you’ll know not to waste hours replacing it.