On my 81 , I have the same problem. I tweek with the Idle screw and raise it about 200 RPMs. The CIS systen should pick up the idle. Mine is disconnected, for I found I get a lot better MPG with it secured and plugged. Mostly only effects the car in cold weather. works without it in warm weather. My car with B21F has a temp. sensor and a switch on my throttle , which feeds a computer . The computer controls an air valve , located top center of the valve cover. This increases / decreases air to the intake Man. to raise or lower the idle. I may fix this system on my car and compair the milage again. It jumped up when I secured this system on my car. Is your AC stock with R 12.? I added the pusher fan mod to mine, and it helped my AC & block cooling. Any suggestions my way for the AC ?

Eck Sheppard 81 242 Portsmouth, Va.

Do not or raise the idle. There is not a solenoid to open the throttle.

There is a compensation system for raising the idle when the compressor is engaged, it may be the kind that increases air intake and tells the computer that it did so. It is different on different models, and I am not sure what system your B21F with its CIS injection system has. Look for a valve thingie on the firewall that has two vacuum lines to it. Maybe one of the lines isn't working right.

Perhaps another brickster will have the exact info.

BTW Does your 3-speed auto have overdrive? A button on the left side of the shifter handle?

There should be an info label under the hood, on the main panel, left side, with a chart of equipment listed. Some in code. If you find it, someone here can translate it,