Not  a mechanic. My light used to come on at idle then go off at 12rpm. Now it is staying on afer driving for about 5min. All guages show good status. All fluids okay. Engine runs smooth. No sign of a problem.

The '81 doesn't really have a lot of computer controls, so it should be fairly easy top diagnose. The symptoms suggest you have an O2 sensor on the blink, but it could also be a problem with the choke, or choke wire.
Pulling code(s) would help, but the codes will only be available while the light is on. Once it goes off, or you turn the ignition off, the code will disappear.
Locate the ALDL connector, which is either right under the dash, by the steering column, or it may be under the ashtray.
Run a jumper(paper clip, or wire) between the "A" terminal, and the "B" terminal. Turn the key on, and watch the check engine(service engine) light, as it will flash any codes. If you see it flash once, pause, then flash twice quickly, that is code "12", which simply means the system is in diagnostic mode. It will flash each codes 3 times, then it will flash the next code, if any.
Since you turned the key off to connect the jumper, it's likely there will be no codes stored, but you can drive the car until the light comes on, then carefully jumper the terminals...just be certain you are connecting the correct terminals first.
If you get any codes, post them up here, and we'll get the info posted on them, and see what we can do to help correct the problem.

                                                           


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Joel Adams
C3VR Lifetime Member #56    
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Joel - Another dumb one, I had this issue on my 81...  Gauges read fine BUT my alternator went. It was over charging. Believe it or not my o2 sensor did not trigger a lamp.

True dat, Kev... The choke wire comes directly off of the alternator, which is what is prolly causing the Check eng. light to come on in that situation. Still would be good to know IF there are any codes being set, as it gives a starting place for diagnostics. However...checking batt voltage, and alternator output should be the first thing to do on any electronic controlled systems. If the reference voltage ain't what it's supposed to be, the sensor/component data ain't gonna be right, either.
Thanks for bringing that up.


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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

It is very rare for the computer chip to be bad.  The chip is located on the ECM which is located in the compartment behind the driver (driver side).  Check the codes but I bet that you have a loose or broken belt somewhere.  I had my engine lite come on with the battery lite and it happened when I broke a belt to the alternator.

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Alwso, the ALDS (Assembly Line Data Switch) may be turned around 180 ndegrees from the picture.  look for the notch between

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terminals.  Then use other side.

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