While driving one of the GT's yesterday (1986 GT, stock V6 no mods, 106K miles) the Service Engine Soon light popped on. I was tooling trough a construction zone and the speed limit was 25-mph (40-kph). After getting through the construction area and back up to 60-mph for a while, the light cleared itself. Later, while driving through town at a low speed, the Service Engine Soon light came back on and stayed on. When I left my office to go home the light had gone out again. It came on again as I retraced my route home. On when the car was being driven slowly and off when up to highway speed for a little while.
I checked for codes when I got home and found that the ECM had thrown a CODE 13 - Oxygen sensor failure. I know this means the sensor is either disconnected or it needs to be replaced but the on and off cycling of the Service Engine Soon light has me wondering if I should be checking for a problem with the Throttle Position Sensor.
I've got spare O-2 sensors but I'm at a loss as how to check or adjust the TPS. Any suggestions?
[This message has been edited by Mike in Sydney (edited 04-15-2021).]