1990 Lemans GSE 4 cyl 2 ltr gas. Starts quick but in temps less than 60 will not idle. When I turn lights,blower,wipers,flashers,fog lights etc on - it raises RPM’s
which allow this rascal to idle by itself. When warm, I can start turning off lights & stuff one at a time. Summer time it starts and
idles normal. Once warm car runs smooth, although at times may chug (in witch case I just turn on my lights & it goes away). Have replaced: alternator (twice), idle speed control sensor (twice), spark plugs, plug wires, distributor cap, rotar, & computer box. This thing has been to 3 shops & 1 internet ‘fixit’ site. If you can figger this out - yoo da man !!!
Have you had the battery tested? Sure it’s a long shot, but it’s free!
I’d suspect at the coolant sensor. If it hasn’t been replaced ever, I’d replace it as they do go bad and are pretty cheap and easy to do.
You can have similar issues if the coolant is low and this sensor is mounted up high in the block.
It’s most likely either the coolant sensor or there’s an air leak somewhere. The mixture must be lean since it happens when cold but not hot, and either problem can cause this. My first guess at fixing this would be looking for a vacuum line that as broken or disconnected, or a vacuum device(like the brake booster) that is leaking. Easy for a mechanic to prove or disprove.