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Unknown Sensor On Throttle Body - '95 Mazda Protege

I just swapped out the throttle body on my car, not because I needed a new throttle body but because the IAC valve I needed was attached to the throttle body with 4 circle-headed philips screws that didn’t want to budge. Anyway, When I went to reinstall everything, I realized there was an extra electrical connection I hadn’t noticed before. I located the sensor it connected to on my old throttle body, removed it, but when I went to install it on the new throttle body I found that the position it was supposed to mount in was occupied by a much smaller allen bolt. This unkown sensor off the old throttle body was too large to fit in the threading of the new throttle body. I stood there staring at it for a few minutes, then said what the hay and just put her all back together again leaving that sensor disconnected. I turned the car on, and it fired right up and revved when I hit the gas. I haven’t tested it on the road yet as I had dropped insurance on the car for the summer and haven’t reinstated it yet.

My question: could anyone tell me exactly what this sensor is, what it does, and why I really do or don’t need to have it connected? (pics below)
From what I can infer, it is a very simple (single-pronged connection) sensor that reads whether the throttle is open or not. There is a “button” that rests on a plate and is depressed when the throttle is closed, and when the throttle opens it lifts the plate and the “button” on the sensor releases. The smaller allen screw on the new throttle body seems to operate as a limit stop, preventing the throttle from “over-closing” when in resting position. Moreover, every throttle body schematic I have been able to find depicts the allen bolt as is on the new throttle body, and I can’t find anything to help me along in my Haynes manual. The closest thing I can come up with is either a coolant temp sensor or intake air temp sensor, but neither of those makes sense to me given its position.
Any help would be much appreciated.

Does the vehicle have a manual transmission?


It looks like you have a heated throttle body. That component appears to be some kind of a coolant temp sensor

Yes, it is a manual.

As I said, I pondered the coolant temp sensor but couldn’t understand why it would be mounted where it was. At any rate, if I replaced it with a throttle body that didn’t have one of these sensors, what kind of effect could I expect?

The throttle body you got could be from a vehicle with an automatic transmission.

That’s not a sensor but a throttle stop. That throttle stop prevents the throttle plate from completely closing when shifting between gears. Because if you suddenly close the throttle at speed this causes a rich mixture. So that stop holds the throttle plate open slightly so this doesn’t occur. It’s an emission control device.


The replacement throttle body was pulled from a '96 Mazda Protege with a manual transmission.
The replacement throttle body also appears to have a “stop” or limit screw that prevents the throttle from closing to a certain degree, but it is no connected to any electricals (rather set in a fixed position with that single allen bolt).

So what does this mean? Should I consider more drastic steps to detach the IAC valve in order to install it onto my old throttle body?

That’s what I’d do.

I always find it better to plug things back in that should be plugged in, than to leave things unplugged.

And by the way, your 95 is OBDI, and the 96 is OBDII.


'95 was the first year the Protege was equipped with OBD2, although I believe it wasn’t “fully” compliant. At any rate, that would only affect whether or not certain codes would register to turn on the check engine light, wouldn’t it?

I hope this doesn’t come off wrong, I’m just trying to understand how this operates.

Are you saying this component receives a signal telling it to push out the “button” or “stop” when you press the clutch pedal? I don’t understand that, as the travel on the throttle is affected by less than 1mm when the button is fully extended from when it is depressed. At any rate, wouldn’t the TPS already dictate to the computer how to regulate the fuel?

This is frustrating to me as I can’t find any schematic that shows this component, and I can’t find it on any of the numerous parts lists I’ve looked over nor can I find anything about it in the car’s manual or the Haynes manual. It almost seems like an after-market addition to me.

I think it’s just a switch to indicate the throttle is closed.
It can be tested with an ohmmeter or continuity tester.