AE 92 trouble codes 25 and 71 please help

[ser3100]

Hey all im getting two trouble codes on my 92 sedan and would like to ask for some helpfull info on fixing the problems. I believe the 25 code is about running too rich and the 71 is about the EGR vavle. I just changed the spark plugs a month ago and went with ngk plugs from pep boys. My car has 280k on the odometer but has been well taken care of. She stilll runs strong but i just wanna get rid of the codes and hopefully she'll run even better. Any helpfull info would be appreciated. Thanks

[90 GP]

Might try pulling egr valve and cleaning carbon deposits out of passages. Also check vac lines going to it. Possibly oxygen sensor is failing for your 25 code.

[ser3100]

Are you refering to the o2 sensor on the header? How hard is it to remove the egr valve?

[Kiwi-Corolla]

Code 25 means it's running too lean, not too rich . It could be the oxygen sensor, injectors, fuel pressure regulator, coolant temperature sensor, or possibly a vacuum or exhaust leak.

[ser3100]

yeah i have a feeling its either an o2 sensor or the coolant temp sensor. Wouldnt that be the same as the thermostat? Reason behind that thought is becuase when my car runs on the freeway it seems that the temp reads lower but when sitting at a stop light or in heavy traffic the temps go up slightly until the engine fan comes on and then it goes back to normal. Correct me if im wrong but doesnt the temp guage normally stay in one spot if the T stat is working correctly?

[Kiwi-Corolla]

Originally Posted by ser3100

yeah i have a feeling its either an o2 sensor or the coolant temp sensor. Wouldnt that be the same as the thermostat? Reason behind that thought is becuase when my car runs on the freeway it seems that the temp reads lower but when sitting at a stop light or in heavy traffic the temps go up slightly until the engine fan comes on and then it goes back to normal. Correct me if im wrong but doesnt the temp guage normally stay in one spot if the T stat is working correctly?

Yep, the temperature gauge is meant to sit on the halfway mark when the engine is at normal operating temperature. Typically a faulty thermostat wouldn't trigger a CEL, but it's worth replacing anyway. The coolant temperature sensor is part of the housing near the throttle body. If this is faulty then it could cause the same symptoms that a faulty thermostat would.

You can check the sensor by unplugging it and checking that 5 volts is available between the connector terminals by using a digital multimeter. If you're getting 5 volts then you can also check the resistance values between the terminals, which change as the engine heats up.