I tried a stomp test for the first time today, no fault codes. About 30 minutes later the car started to hesitate terribly when trying to accelerate as though it was running out of gas. After pulling over at a gas station I did a stomp test, now it is showing 1221 (O2 sensor1). I put some fuel in and drove back to work, now my check engine light is on continuolsy however it seemed to run okay for those 4 miles back. Is this something related to the first stomp test or is it just coincidence?