I heard that the air temp sensor hooked under the plenum isn't necessary for the engine to run. What are the facts?

Thanks,
Buck

That’s Factual.

There are a lot of parts that can be eliminated. I happen to be in the camp of eliminating all of it (aar, csv, etc etc., SOO satisfying to eliminate)... But know what you are doing first. And what your intentions for the car are about.

If your car is nice, don't. Because they are growing in value and having everything in place matters for value.

The air intake sensor (T1) has an impact on mixture. Removing it is going to bias your car toward a richer mixture. I gather a lot of mechanics back in the day would simply disconnect it to "solve" other issues that would be causing a customer's car to run lean. If you remove it, rather than simply disconnecting, you'll have a vacuum leak unless you fill that spot.

Why are you removing it?

Maybe I didn't call the switch in picture correct. What does the thermo switch do? Does it have anything to do with the air temp sensor in the plenum? I am trying to understand the D-jet system better. My experience so far is that D-jet hates vacuum leaks. I have taken care of that and have the engine running better. But I have disconnected the air temp sensor and have been told that the thermo switch is unnecessary. I would love to reconnect the air temp sensor but the engine dies after warm up.

I am trying to get the idle up on the car between engine starting and when engine gets warm. The idle will die during this interim period. Right now with the air temp sensor on the plenum disconnected the idle drops from under 1000 rpm at start up (cold) to nothing after about 2 minutes. It then idles about 500 rpm after the engine warms up and doesn't die. I want to move that up a bit so I played with the ecu knob and the idle mixture screw on the throttle body. I now have 1200 rpm at start up and 1000 rpm after warm up without the stumbling and dying during the interim period.

What I would like to do is bring the air temp sensor on the plenum back on line but want to know how and when to do this. Do I put the connector back on the air temp sensor before starting and play with the ecu knob and idle screw on the throttle body when the engine warms up or should I connect the air temp sensor once the engine is warm? Just trying to figure out how to get the air temp sensor back on line.

BuckClick to view attachment

I know I am talking about two different sensors/switches. The picture shows the location for the thermo switch. Want to know how this works and if it can be unplugged. The temp sensor 1 in the plenum is what I want to bring back on line.

Ok, yes, these are two separate things. The bracket in your pic is for the thermotime switch. That sensor is supposed to detect a cold ambient situation (e.g., less than 35 or 40 degrees) that will require more fuel at immediate startup. It then activates the cold start injector on the other side of the plenum in this situation. If you don't live in a cold environment, you don't really need it. Even if you do, you can get the car started without it.

It sounds like you're running too lean and that's why it's dying when cold. Fuel pressure may be too low, or injectors or filter may be clogged and need cleaning / replacing.

Make sure your auxiliary air valve (AAR) is hooked up and functioning correctly. That should help with warm up. Before fiddling with the ECU knob, you should make sure the following are correct:

1. Timing
2. Fuel pressure
3. Throttle position sensor (calibrated)
4. T2 (Cylinder Head Temp sensor) is working properly and that you have the right CHT / setup for your car. What year is this? I think '73's required the ballast resistor.
5. Also, verify you have the right ECU/MPS/CHT combination for your car.

Then hook the T1 sensor back up, get car warm and use a combination of air bleed bypass screw on throttle body and ECU idle mixture adjustment knob to get it where you want it.

I believe you are pointing to the thermo switch. This controls the cold start injector. At a low temperature, the cold start injector is active when the starter is engaged.