E30 Early 1987 Idle Control Module/Idle problem

[Brendan Daly]

I'm trying to debug an idle "hunting" problem. The problem only occurs when the engine is heated up. When the engine is started the idle is good, but after the engine heats up it suddenly start hunting up and down. I have checked all the usual suspects: vacuum leaks, changed the idle control valve, checked the throttle position switch, coolant temp switch, all to no avail.
However, I have been unable to figure out where the "temperature" switch that goes to pin 10 of the idle control module is located. I have seen it referred to as "air temperature switch" . It is supposed to be closed below 18F and open above 39F. I cannot find any reference to it location anywhere. I'm unsure as to the purpose of this switch. Can anybody help with the location and/or purpose ?

[Barbeemer]

The air temperature sensor is inside the mass air sensor between air filter and throttle body.Have you check idle control unit under dash beside ECU/

[Brendan Daly]

I will check the sensor ... thanks for the location.
I have changed the control unit with one I got in the junk yard, but no change in behavior. I also broke open the old unit to look inside the unit. There were no signs of any components being burnt.

Brendan.

[Barbeemer]

How about the fuel pressure regulater,pinch return hose to hold in pressure,see if it makes a difference,take off vaccum line ,hold finger over line,any difference?

[Freebirdrebirth]

Also try the airflow meter, they wear and cause a lean mixture at idle. the o2 would have a hard time compensating and so it hunts. my dad showed me a way to open them and adjust them from the top, but maybe swaping it would be easiest.