Anyone understand why the CIS system has a coolant temp sensor? This is a switch type sensor. The idle speed does not change on these engines, cold, hot, AC on/off, neutral or in gear. It is a two-wire sensor with red and blue wires running through the right side gray connector to the CIS computer. My only thought is that, depending on temperature, the air valve may be held in a different position when the throttle is off idle. Not sure what that would achieve.

Continuous Injection system or Constant Idle Speed system

Here is the schematic from the 1981 Wiring Diagrams green book.

The early CIS (Continuous Injection Systems) went with a thermal time switch and not the coolant temp sensor. I have an early CA '78 242GT that incorporates the coolant temp sensor with an O2 sensor and frequency valve on the K-jet injection diustributor. The rest of the US during those years had and EGR system without the O2 sensor. In this case the thermal time switch was given a voltage for a short time period (~12-30 sec) while cold, the same as the auxillary air valve, and was shut off after the engine warms up. Together, they are part of an electro mechanical choke system, that enriches the mixture via the FPR.
The system that uses a coolant temp sensor and frequency valve with O2 sensor is a dynamic engine management fuel mixture control system. The frequency valve which controls the fuel delivery is governed by the ECU from the coolant temp and O2 sensor response, 100% of the time. Some of these systems used the auxillary air valve which is not acting like a constant idle govenor, and some used a constant idle air control valve. This system is a very nice one for the early B21F engines, and is very similar in principle to the LH 2.2-2.4.
--
'89 245 Sportwagon, '04 V70 2.5T Sportwagon

Hello,
If you have a Constant Idle System, the coolant sensor is telling the ECU what idle speed to set based on the engine temperature. The colder the coolant the higher the resistance it shows to the ECU. The ECU then sets the air control valve to control idle. The ECU also reads the ignition pulses like a tach to know what the idle speed is. As the motor warms up, the resistance decreases to the ECU which slows the idle down. When the motor reaches operating temperature the ECU reads the ignition pulse to control idle. If you want to test this, let the motor warm up. Stop the motor and remove the plug from the temperature sensor. Restart and the motor should go to a very high idle. Stop the motor and put the connector back on the sensor and restart. It should go back to low idle. Hope that helps.

Mario

Anyone understand why the CIS system has a coolant temp sensor?

It's for the control pressure regulator (aka warm up regulator).
--
'80 DL 2 dr

I thought the control pressure regulator was sensing the temperature itself?

Okay, that is correct after the engine warms up, according to Probst.
--
'80 DL 2 dr

The CPR does depend on a heated bi-metal spring. Thus it has an electrical connection. I was thinking this was controlled by a temp sensor but in looking at a very fuzzy K-Jet diagram that doesn't seem to be the case.
I'm now thinking that 81242DLB21FCA is refering to the thermal time switch for the cold start injector.
Better wait for one of the experts to reply.
--
'80 DL 2 dr

I was looking at the CIS schematic in the 1981 Green Book. The question arose from a post about a temp sensor causing idle problems. The sensor only goes to the CIS control box mounted in the passenger side panel. I'll post the drawing when I get home tonight (PST).

I've just realized that you are refering to the Constant Idle System. I thought you were being redundant when you used the acronym CIS (well...it does happen sometimes). I should have picked up on the blue and red wire reference.
Scratch everything I said earlier. I'm not familiar with this system (no constant idle feature on my car).
I'm going to look at my wiring diagrams too. I could stand to brush up on this subject.
--
'80 DL 2 dr