cold start

Circuit theory: When starting a cold engine, the cold start injector squirts fuel into the plenum for a few seconds and a vacuum control turns a lever allowing additional airflow into the plenum to raising the idle speed. (this later is often plugged to lower speed from 3000 to 1200-1500 rpm.)

Components in the circuit include 1 or 2 thermostatic switches, one under the overflow tank controlling the dash light and the idle speed electrovalve. Additionally some 1980-1 cars have a thermostat to kill juice to the cold start injector when warm. There is also a thermo-time sensor in the valley to limit injector squirt time.

BUT dash light off with a cold engine together with continuous high idle...that's two problems, not one thing which failed. Problably someone has helped it along with an attempted 'fix'. Is this car new to you, perhaps altered by the previous owner? Or was it ok last season and did this condition recently happened? Or have you messed with anything in the engine compartment like changed plugs?

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Reason I asked about the plugs, someone recently accidentally unplugged the thermostat connector under the overflow tank when they changed them. So check there first.

Given enough time, does the idle ever come down to normal?

 

Ignoring absence of cold light for now...

Photo courtesy TonyK shows the cold start air valve which raises idle rpm. It is operated when 12v applied to the fast idle electrovalve at upper left in photo which is a vacuum valve. It allows vacuum to go from plenum to electrovalve to the cold start air valve. The fast idle electrovalve gets 12v from key and ground from thermostatic switch which you just checked.

Back at the car, with attention to the air valve...see if it is stuck in the open position and that the vacuum hoses are correct. Generally poke around there with a can of WD-40, sucking on the vacuum hose to the air valve. Once you free the device to open and close properly, note the large molded 90° air hose it controls. It is this hose which when fully opens causes the 3000 rpm idle. It can be restricted by inserting and object to reduce the idle speed to a more reasonable 1200-1500.
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