Using OBD1 scanner when car us running

I just ordered a obd1 scanner to check a code on my 1989 5.0. Can i plug it in while the car is running. Im a new owner of the car and the check engine light comes on about 10 min into my trip. But when i turn the car off and back on the check engine light goes away

Im sure its something to do with the 02 sensor because one of them has the wires missing and another is broken but still attached (hope my harness is still there). But im also getting a low idle speed 600 or so but normally when first starting and settling its around 750rpm. Hoping the code reader i ordered lets me know what issues i have and why i have a low idle that feels as if its about to die which it did one day while braking downhill

Thanks for the info. I already have the page on surging idle save for me to look at after the codes. It looks like great info for troubleshooting

Mustang5L5 said:

Even though the check engine light goes away, the code should be stored in the Continuous memory codes. Just run the codes while parked and engine is off. After you get the KOEO and CM codes, start the engine and run the KOER codes. If your CEL comes on, it should be stored in CM

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Sweet

Thanks for the info. My eader will be here wednesday and i will pull the codes. Hopefully will give me a good starting point